fixed MSVC12 compile error & adapted plugin install structuring
Merge pull request #28 from dgimb89/master

MSVC12 compile fixes & small plugin restructuring
Move INSTALL_PLUGINS[_DEBUG] variable to the main CMakeLists and remove assumption that are not valid on all operation systems.
Fix plugin deployment for linux
Remove OSG-include from OsgKeyboardHandler to make it possible to include the header in the context of glbinding.
Fix compilation on Windows (MSVC2013)
adjust find scripts of gmock and gtest to search in default build directories of MSVC (update from cmake-init)