Add multisampling support in samples

This series of patches improves the MSSA support.
The first patch allows to use MSSA with a standard forward rendering pipeline if the default FBO supports multisampling.
MSSA options are added in the samples. The multisampling can be changed interactively using the F6 and F7 keys. When the mutlisampling value of the default FBO changes, the window is recreated. Multisampling is supported in the forward pipeline and HDR, but not in the deferred.

Please review.