Misc small enhancements / bug fixes

- movie helper: fixed possible warnings if using error_reporting(E_ALL)

- legal_file helper: changes to reduce warnings/errors, new get_types_by_extension merged function (similar to get_extensions merged function), new optional extension-searching arguments for get_photo_extensions, get_movie_extensions, and get_extensions (similar to get_photo_types_by_extension and get_movie_types_by_extension functions)
- uploader controller: use new legal_file enhancements
- item model: use new legal_file enhancements
- server_add controller: use new legal_file enhancements
- admin_watermarks controller: use new legal_file enhancements

- graphics helper: fixed possible warning if using error_reporting(E_ALL)

- data_rest and file_proxy: make comments/structure/format more consistent between them
- file_proxy: disallow album resizes (don't exist), make album thumbs have correct mime