Add support for manual addition of breaks

[SomeDer]

Description
Add support for manual addition of breaks from work.

Possible implementations
plan break -i 1 -t 0.5 -d 0.5 will add a 30 minute break once half of task 1 is done.

• -i is the task ID
• -t is how long the break is (hours)
• d is how much of the task is done before the break (default 1, which is all of it)

Additional detail
Automatic breaks will be added by #12