update the TODO
glapi: fix memory leak from not freeing a string
display: allow the user to try and choose the GL api we use via env variable

GST_GL_API=opengl,opengl3,gles2,gles3
move sink-specific stuff from GstGLDisplay into glimagesink
display: remove list of upload and download objects

and only create an up/download object when needed.
display: move most of the code into utils for sorting later

This contains a hack that essentially requires one GstGLDisplay
per process.
display: move context creation into window
x11: fix segfault if the x11 backend is instantiated but not used
x11: don't segfault if destroy_cb is NULL
Use gst_object_[un]ref so we can get refcounts in the log
x11: don't shutdown in _finalize

The window's loop could be still running when _finalize is called
and if we destroy the display connection it will never be closed.

Add _open and _close vfuncs to GstGLWindow so that subclasses can
start up and shutdown at the right time.
display: move activate_context into utils
display: move error_message to utils
display: a cleanup and removal of old code