GLSLEditor: Remove needlessly exported symbols

... and move code into Internal namespace.

Change-Id: I02a90c33db0ffe574af43bdb8d8e37b4159f8f0f
Reviewed-by: hjk <hjk121@nokiamail.com>
Python: Do not export symbols

Nothing depends on this plugin, so these exports are not needed.

Change-Id: I7a6c1c6fd1dd355c904d2dcb6d3f0522cf30adcd
Reviewed-by: hjk <hjk121@nokiamail.com>