1. A key can either be an ssh user key or a deploy key. It cannot be both.
2. If a key is a user key - it can only be associated with one user.
3. If a key is a deploy key - it can be used in multiple repositories and the permissions it has on those repositories can be different.
4. If a repository is deleted, its deploy keys must be deleted too.
We currently don't enforce any of this and multiple repositories access with different permissions doesn't work at all. This PR enforces the following constraints:
- [x] You should not be able to add the same user key as another user
- [x] You should not be able to add a ssh user key which is being used as a deploy key
- [x] You should not be able to add a ssh deploy key which is being used as a user key
- [x] If you add an ssh deploy key to another repository you should be able to use it in different modes without losing the ability to use it in the other mode.
- [x] If you delete a repository you must delete all its deploy keys.
Fix#1357
* add util method and tests
* make sure the title of an issue cannot be empty
* wiki title cannot be empty
* pull request title cannot be empty
* update to make use of the new util methof
* add migration and basic UI for changing a user's theme
* update user themem
* use right text on button
* load theme based on users' selection
* load theme based on users' selection in pwa too
* update sample config
* delete older theme loading
* implement AfterLoad to set users' theme properly
* set up default theme when creating a user. This uses the installation wide theme
* use flash messages for error
* set default theme when creating a user from the cli
* fix @lunny review