put Daily and To-Do tabs at top and bottom - fixes https://github.com/HabitRPG/habitrpg/issues/3827

Moves the code for the To-Do tabs and Dailies tabs to a mixin and puts them at the top and bottom of each column.

The mixin takes a "position" parameter (with "top" and "bottom" values) to allow customisation of the appearance (currently only used on the To-Dos completed tab to show the delete button at the bottom only).

![screen shot 2014-10-10 at 9 11 30 am](https://cloud.githubusercontent.com/assets/1495809/4585788/778fa616-500b-11e4-9ba4-6ab9d65f7a5c.png)
![screen shot 2014-10-10 at 9 11 43 am](https://cloud.githubusercontent.com/assets/1495809/4585787/7783463c-500b-11e4-8760-c890909ad756.png)