Return day values from habits index.

Removed @days_in_month variable and now use the habits themselves,
both to know how many days to display and whether the habit was
followed on that day.

: #ui #test #refactor #angular
Rename cucumber givens to use active voice.

: #test #refactor
More tweaks to cucumber steps.

: #test
Add feature to set dates on habits.

Created a HabitDate class that relates to Habits. That class has a
date attribute, so the final relationship is User->Habit->HabitDates.
Return flags from habit dates on index.

: #ui #db #angular #test #feature