[WIP] refactor Controllers to improve UI

 - Replacing recently added thrown Exceptions with appropriate return/redirect and information to user.
 - Modifying docblocks where appropriate
 - Replacing deprecated functions where possible.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| Refs tickets  | #1413
| License       | MIT
| Doc PR        | -

 - [x] Admin
 - [ ] Blocks
 - [ ] Categories
 - [ ] Extensions
 - [ ] Groups
 - [ ] Mailer
 - [ ] PageLock
 - [ ] Permissions
 - [ ] Search
 - [ ] SecurityCenter
 - [ ] Settings
 - [ ] Theme
 - [ ] Users

could really use some help with this... @cmfcmf @rojblake