Updating DELF version: 2.1 (#8473)

* Merged commit includes the following changes:
253126424  by Andre Araujo:

    Scripts to compute metrics for Google Landmarks dataset.

    Also, a small fix to metric in retrieval case: avoids duplicate predicted images.

--
253118971  by Andre Araujo:

    Metrics for Google Landmarks dataset.

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253106953  by Andre Araujo:

    Library to read files from Google Landmarks challenges.

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250700636  by Andre Araujo:

    Handle case of aggregation extraction with empty set of input features.

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250516819  by Andre Araujo:

    Add minimum size for DELF extractor.

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250435822  by Andre Araujo:

    Add max_image_size/min_image_size for open-source DELF proto / module.

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250414606  by Andre Araujo:

    Refactor extract_aggregation to allow reuse with different datasets.

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250356863  by Andre Araujo:

    Remove unnecessary cmd_args variable from boxes_and_features_extraction.

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249783379  by Andre Araujo:

    Cre...

research/delf/DETECTION.md

 ## Quick start: landmark detection
 
+[![Paper](http://img.shields.io/badge/paper-arXiv.1812.01584-B3181B.svg)](https://arxiv.org/abs/1812.01584)
+
 ### Install DELF library
 
 To be able to use this code, please follow

research/delf/EXTRACTION_MATCHING.md

 ## Quick start: DELF extraction and matching
 
+[![Paper](http://img.shields.io/badge/paper-arXiv.1612.06321-B3181B.svg)](https://arxiv.org/abs/1612.06321)
+
 ### Install DELF library
 
 To be able to use this code, please follow
@@ -76,12 +78,10 @@ $DISPLAY environment variable`. To fix this, one option is add the line
 see the discussion
 [here](https://stackoverflow.com/questions/37604289/tkinter-tclerror-no-display-name-and-no-display-environment-variable).
 
-
 #### 'skimage'
 
-By default, skimage 0.13.XX or 0.14.1 is installed if you followed the instructions. According to [https://github.com/scikit-image/scikit-image/issues/3649#issuecomment-455273659]
-If you have scikit-image related issues, upgrading to a version above 0.14.1 with 
-```
-pip install -U scikit-image
-```
-should fix the issue
+By default, skimage 0.13.XX or 0.14.1 is installed if you followed the
+instructions. According to
+[https://github.com/scikit-image/scikit-image/issues/3649#issuecomment-455273659]
+If you have scikit-image related issues, upgrading to a version above 0.14.1
+with `pip install -U scikit-image` should fix the issue

research/delf/INSTALL_INSTRUCTIONS.md

@@ -2,6 +2,8 @@
 
 ### Tensorflow
 
+[![TensorFlow 2.1](https://img.shields.io/badge/tensorflow-2.1-brightgreen)](https://github.com/tensorflow/tensorflow/releases/tag/v2.1.0)
+
 For detailed steps to install Tensorflow, follow the
 [Tensorflow installation instructions](https://www.tensorflow.org/install/). A
 typical user can install Tensorflow using one of the following commands:

research/delf/README.md

 # DELF: DEep Local Features
 
+[![TensorFlow 2.1](https://img.shields.io/badge/tensorflow-2.1-brightgreen)](https://github.com/tensorflow/tensorflow/releases/tag/v2.1.0)
+
 This project presents code for extracting DELF features, which were introduced
 with the paper
 ["Large-Scale Image Retrieval with Attentive Deep Local Features"](https://arxiv.org/abs/1612.06321).
@@ -18,6 +20,8 @@ and [NEW] code for model training.
 
 If you make use of this code, please consider citing the following papers:
 
+[![Paper](http://img.shields.io/badge/paper-arXiv.1612.06321-B3181B.svg)](https://arxiv.org/abs/1612.06321)
+
 ```
 "Large-Scale Image Retrieval with Attentive Deep Local Features",
 H. Noh, A. Araujo, J. Sim, T. Weyand and B. Han,
@@ -26,6 +30,8 @@ Proc. ICCV'17
 
 and/or
 
+[![Paper](http://img.shields.io/badge/paper-arXiv.1812.01584-B3181B.svg)](https://arxiv.org/abs/1812.01584)
+
 ```
 "Detect-to-Retrieve: Efficient Regional Aggregation for Image Search",
 M. Teichmann*, A. Araujo*, M. Zhu and J. Sim,

research/delf/delf/python/detect_to_retrieve/DETECT_TO_RETRIEVE_INSTRUCTIONS.md

 ## Detect-to-Retrieve instructions
 
+[![Paper](http://img.shields.io/badge/paper-arXiv.1812.01584-B3181B.svg)](https://arxiv.org/abs/1812.01584)
+
 These instructions can be used to reproduce the results from the
 [Detect-to-Retrieve paper](https://arxiv.org/abs/1812.01584) for the Revisited
 Oxford/Paris datasets.