add/renew context and context format classes
Merge branch 'master' into context

Conflicts:
	source/gloperate/CMakeLists.txt
fix glfw find script
fix cubescape example
revisit abstract context, context format and impl glfw context
Merge branch 'master' into context

Conflicts:
	source/gloperate/CMakeLists.txt
refine context classes
* make current and done current are mandatory for abstract context
* add string information
* refine warning output for format verification
* fix and refine swap interval setter
* fix and refine format defaults
* add version retrieval with fallback
* replace glfw induced gl calls with glbinding
* refine comments
Merge branch 'master' into context

Conflicts:
	source/examples/ViewerGLFW/main.cpp
	source/gloperate-glfw/include/gloperate-glfw/Window.h
revisit PluginManager
* unify PluginLibraryImpl impl
* unify scan impl
* fix path separator issue
* use more consistent (with other hpicgs projects) var names
* reduce output when everything succeeds
refine plugin meta
reduce warning level due to libzeug inheritance dominance issue
fix window init and format
Merge branch 'master' into context

Conflicts:
	source/gloperate-glfw/source/WindowEventHandler.cpp
	source/gloperate/CMakeLists.txt
review plugin concept
* simplify function names
refine qt examples cmake
allow multiple search paths for plugin manager and explicitly support reload
remove keys in favor of glfw keys and use enum class for event type
rename main loop class to application  and rename example project
prepare qt review and update cubescape demo
Merge branch 'master' into context

Conflicts:
	source/examples/viewer-glfw/CMakeLists.txt
	source/gloperate/CMakeLists.txt