*IMPORTANT FIX* Fixes possible crashes/segfaults when converting OpenGL image representations to local image representations:
 * ImageRepresentationLocal::tryConvert() does not deadlock anymore when called from OpenGL context and converting from GL representation
 * Fixed possible double deletion after converting from OpenGL to local representation due to ambiguous pointer ownership
 * fixed possible out of bounds array write in tgt::Texture::downloadTextureToBuffer()