TextEditor: Move SnippetsEditor to new editor construction scheme

Change-Id: I10612d86b6a634e7370c1a29507f709132f4e54b
Reviewed-by: Christian Stenger <christian.stenger@digia.com>
GlslEditor: General editor related code consolidation

Merge editor files, convert to new editor setup scheme,
fix names according to convention.

Change-Id: I13682c0c86ac22e4cba3a826505248c7a0291a55
Reviewed-by: Christian Stenger <christian.stenger@digia.com>