[bug 1077359] Deactivate Malayalam (ml) locale
Move old KB dashboard readouts to new url
[bug 1048774] Show form validation errors for PMs
[bug 1048774] Add character counter for private messages.
[bug 1081652] Only update session timezone if editing own profile.
[Bug 1074959] Add metadata API.

This isn't as nice as I wanted. The metadata field of questions is a
list of objects in the API. Semantically it should be a dict, but I
couldn't get DRF to play nice with writing in that format. There is some
support for writing directly to the object with POST and PATCH, but it's
kind of derpy, so I also added endpoints for `set_metadata` and
`delete_metadata` that work intuitively for single items.