ToDo Functionality#176

This is a feature for the ability to add ‘to-do’s’ to cards, so that they get checkboxes next to them which can be ticked or unticked.

Once above has been implemented a next step could be to create a view whereby all todo’s can be viewed in one list with columns alongside the view to link to the table and card in question. Also the ability to set a due by date, and sort by due date would be useful.

Also related to #13