[feature] - user photo

### What does it do ?

This is a WIP (mostly awaiting for feedback) to handle user profile photos.

It makes use of Media Sources (using the default one per default, but configurable using the `photo_profile_source` system setting -- expecting a media source ID).

### Why is it needed ?

There currently is no user interface to manage `modUserProfile.photo` (which is used in the manager -- user photo -- and could potentially be used anywhere else)

### To do before merge

- [x] create lexicon string for the system setting
- [x] replicate the UI on security/profile so users
- [x] put photo "retrieval" logic in `modUser` (since it might be useful for developers)
- [x] squash commits

### Related issue(s)

Closes #11824