Renamed "gl_context" to "context"

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>
Added more structure to X11 backend

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>
Abstracted the rendering context data type

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>
Propageted changes to WinDOS port

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>
Removed "core" argument from context creation function

Neccessary information can -and should- be deduced from window argument

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>