* Moved the context handling stuff into gpencil_utils.c
* Moved the datablock and layer operators out into their own file too. Again,
these weren't related to the other stuff that much
* Split the GPencil to Curves operator out into its own file (gpencil_convert.c).
This was quite a massive blob of code (48kb) that was not that related to the
other operators still in that file (gpencil_edit.c)