Support Video Uploads

[lou-k]

The current helper functions are for images only.

This should be a relatively simple change:

• Update create_new_revision_from_file to accept a subtype parameter
• Change upload_image_file to use the content_type to guess the subtype parameter
• Change the function names upload_image_file and upload_image_file_if_not_exists to upload_media...

Note that there is a 200MB upload limit that we should address in a future issue.

[lou-k]

fixed!