GitLab

Per workshop dryrun, leave OpenMM:: namespace prefix explicit to clarify what's part of OpenMM and what's not.

License header changes; force duplication factor to 4; fixed potential problem w/ Shake -- if no constraints, pgm crashes

I'm checking in very early attempts at OpenMM Hello World examples so Chris and I can work on them together.

Eliminate some VC++ build problems via the usual expedient of explicit casts from unsigned to signed and from double to float. TNT Arrays apparently can't be indexed with unsigned because VC++ finds something ambiguous then above their operator[] methods.

(1) Made Platform::loadPluginLibrary() for Windows leave the end user alone if a failure occurs -- was throwing up an error box.
(2) Made Platform::loadPluginsFromDirectory() on Windows find only .dll's. 

Added Platform::getDefaultPluginDirectory().  Plugins are now installed into .../openmm/lib/plugins.