Editable Daily Review Goal

[cblanken]

Currently, only the "Reading" and "New words" goals are editable. I would also like to edit the daily "Reviews" goal too. It's unlikely I'll ever fully catch up on daily reviews from the whole backlog of marked words, so limiting it to a more manageable number would be nice.

I don't know about the backend, but the UI would probably be a copy+paste of the existing daily goals edit icon and popup modal.

[simjanos-dev]

I also had this one in mind. I'll add it sometime when I'll have time, it will take some back-end work.