Merge pull request #195 from pleroy/InterfaceTest

Mock-based test for the interface
Testable plugin.
Test failing.
Test.
Visual Studio, I hate you.
Property fixes for LLVM.
gMock doesn't know about C++11
Properties
Warning cleanup.
Merge pull request #196 from pleroy/PluginTest

Add minimal support for testing the plugin with a mock n-body system
I haz a test
Centre
Stronger test
loop
another useless warning bites the dust
Merge pull request #197 from pleroy/OED

Centre
2 blank lines in a row...
after pleroy's review
Pass the quantities by reference.
fix lint, update linter, sort useless warnings...