* Initial KTX1/ETC2 support
* Conditional glad include
* remove unused function
* define glenum for non opengl build
* remove unused param
* fix qtbuild
* change ktx format to enum
* use nullptr
* ktx: support the same etc2 formats available in amd compressonator
* add comments and missing include
* correct flag type
* clarify variable name for clang
* cleanup
* update glad loader to GL4.3
