texture2D is deprecated

fixed the screenquad in coreprofile mode by using GL_FRONT_AND_BACK

See merge request !43

as it is a screenquad it should make no difference for compatibility
profiles so no check for opengl version here

Fix core profile incompatibility

See merge request !41

remove this fix as soon as the QPainter problem for embedded logger is
solved

value

vertex_array_object is supported function now always returns true on opengl contexts with version 3.2 or higher

stopped using glew on OSX, because it did not load core profile functions properly. use gl3.h instead. This causes a warning, because gl.h is also included, remove gl.h as soon as we don need to support compatibility contexts anymore.

added functionality to query exensions the modern way to ACG
use this function in about widget to display supported extensions.

removed chck for ARB_vertex_buffer_object as it has become part of opengl spec in version 1.5 and is not listed as extension by some drivers (e.g. all apple drivers)

do not use generate mipmaps as texture parameter in core profile
call glGenerateMipMaps instead

 setting in  CoreWidget, which still userd compatibility profile even when core profile was set via cmdline

also fixed shaderprogram 0 assertion from QOpenGL branch in coordsys
node

specifically:
 initialized glstate properly
 moved various compatibility calls to if branches
 use previous VAO properly in ACG
still to go for the nodes

Fix the warning about changing defaultFormat at startup of openflipper

See merge request !39

this probably breaks compatibility to undocumented writings like
--b --batch /batch etc.

initialize settings before parsing command line options.
prevent double initialization.

fixNameClash

See merge request !40

name does not matter

afterwards to prevent setting the default SurfaceFormat multiple times