[Feature/Improvement] Rest timer

**Purpose:**

To have a rest timer type were it will be a timer only for rests and not the workout set.

**More details:**

Here is an example of a workout...

- 10 Second countdown
- Set 1
- Rest 2:00
- Set 2
- Rest 3:00
- Set 3

There is not countdown timer on sets, instead a "Done" button will be displayed to notify the timer that the set it done and then continue on with the rest timer that follows. Then the next set will start and will not continue on until the "Done" button is pressed and so on.