TodoList - Changing Selection Style

- Setting the ‘None’ style so that it won’t put a gray rectangle over
our pretty cell.
TodoList - Unslide others when editing new cell

Want to ensure that if the user tries to edit a cell, then all cells
will move back to their original positions. This ensures that any cells
that were previously “swiped left” and are still in that state, will
revert back to the unswiped state.

- Updating TableVC to add method moveOtherCellsBackToOriginalPositions.
- This new method is then called from all methods that result in some
sort of editing on a cell i.e. swipeCell and didSelectRowAtIndexPath.
TodoList - Fixing bug in if statement

- Changing condition when checking whether to hide change priority
buttons!