[feature suggestion] Numerical goals

[ClaymeCall]

I was thinking that it could be helpful to be able to set goals measured by other things than time, like count of executions.

Example: I want to practise showing up to the gym rather than having a certain duration of training. So I could set a weekly numerical goal for the task "Gym" that would simply count how many times I started the task, rather than how much time it was active.

[ClaymeCall]

This could synergize with what I suggested in Issue#42 (maximum goals) where we could set a maximum number of times to do a certain task.

[Medvedev91]

Useful feature. Added to the backlog.