Add quick selections for commonly used habit frequencies, such as "every day" and "every week"

[iSoron]

The current "create habit" dialog asks the user for a period of time and how many repetitions should be performed. For new users, it is not immediately clear how does this work. Also, for most of the habits, this much flexibility is not really necessary.

As suggested in #1, the dialog could have some quick selections, such as "every day" or "every week", in addition to a "custom" option. Selecting "custom" would then hide the quick selections, and reveal the current, more advanced "x repetitions in x days" form.