Write custom levels to individual json-formatted .level files

Instead of writing a database migration task, I intend to migrate the existing level set directly from the level-builder data as follows:

1.  Merge this feature into levelbuilder first (note: test runner will fail on seed)
1.  Generate the initial set of custom level files from the server data
1.  Delete old custom_levels.json
1.  Commit and push file changes (note: test runner will pass)
1.  Merge this feature plus the file-change commits together into finished
the name "process file" implies to me that it is reading the file, however this function is for writing. Maybe rename it to something like filter_level_attributes_for_writing_to_file (or something of that nature that is not a mile long)