improvements to translation message generator

improvements to translation message generator

- for rna stringsinclude the path as comment, eg:
  #~ bpy.types.VertexGroup.name

- skip strings like %dx%d or -X.

- for strings extracted from python scripts include file:line reference as with C files.

- have messages in order they appear in the file, files and classes sorted so it reads more logically.

- extract these comments from the messages.txt file into the pot file.