GitLab

* Replace SimTK-containing file headers

* Update file headers for new Tinker reader files added

* Reference platform supports nested virtual sites

* Common platform supports nested virtual sites

* Fixed force distribution from nested virtual sites

* Fixed test failures

* Prevent child integrators from accessing deleted context

* Prevent reading property names from nullptr platform

* Don't check properties in a loop, but only when there's a Platform

* Clarified condition in "if" block
Co-authored-by: Peter Eastman <peter.eastman@gmail.com>

* DrudeLangevinIntegrator has getSystemTemperature()

* DrudeNoseHooverIntegrator has getSystemTemperature()

* StateDataReporter reports system temperature for Drude systems

* Fixed incorrect return type

* Allow querying current step count

* Fixed error building Python wrapper

Updated Context::getParameter() and Context::setParameter() error messages to also print name of incorrect parameter to aid debugging.

Added missing required kernel names (ApplyConstraintsKernel and VirtualSitesKernel) to check for platform capabilities, since these kernels are initialized in the next code block.

Converted the routine for identifying molecules from a recursion to a loop.  This avoids stack overflows with very long linear molecules.