Removed noexcept from functions in SettingStack
Updates in Context and ClientContext

- Viewport, scissor test and stencil test-related functions were added.
- Renamed some of the base classes of ClientContext.
- Minor updates in context::SettingStack.
Merge branch 'develop' into develop-with-eagine

Conflicts:
	include/oglplus/client/setting.hpp
	include/oglplus/context/scissor_test.hpp
	include/oglplus/context/viewport.hpp