Add task progress tracking/introduce "goals"

I think it's very useful to track the progress of a repetitive simple task, which user intends to do N times. These are typically some "goals" or something similar: for example, I'd like to solve 300 problems on Leetcode. Making this task recurring does not make too much sense, because:

* I'd like to track the number of task completions (i.e. how many times I actually solved the problem)
* I do this whenever I have enough time, not daily, weekly or anything; I'm more interested in basically seeing how far I'm from completing this "goal" whenever I look at my task list

This might benefit those setting goals for themselves or those willing to keep track of the number of repetitions of some pretty small task for a long period of time.

This is something I've been looking for in the other task managers and similar systems.