Bug 903960 - [SMS] Switching to message view when selecting left side of the message

- Fix
    - Changed the left position of the label to take up the whole space
    - Removed the translation and translation transition from the `<label>`
    - Added translation and transition to the `<span>` with the checkbox itself
    - Separated the translation transition for the `<p>` so it moves back gracefully
- Tests
    - TBD in another bug