Handle habit collection as a NSMutableDictionary
Add a header view that controls the date selection for the content table

* Add buttons for change the selectedDate
* Add label to display the selectedDate
* Change content of the table depending on the selectedDate
Renamed `currentDate` to `selectedDate`
Merge pull request #1 from fespinoza/add-day-selector-for-view-table

Add day selector for view table