Each implementation of *Application::Configuration will have different
methods tailored to feature set of the underlying toolkit. Currently
each windowed application's Configuration has only window title (except
NaClApplication) and window size. WindowlessGlxApplication has empty
class. More features will come later. Also created introductionary
documentation for Platform namespace.
Because with NaCl WindowContext doesn't make sense anymore, the classes
are now renamed:
* Contexts namespace -> Platform
* *WindowContext -> Application
Hopefully this is (one of) last crazy renaming runs.