Assign Skill Attribute with Todoist Labels

In HabitRPG, in User > Stats & Achievements > Attributes, you can choose to allocate skill points based on task activity (where you assign a task an attribute: str, int, ect).

This PR will allow a user to assign attributes to tasks by typing labels, like so:

![screen shot 2014-08-31 at 6 39 21 pm](https://cloud.githubusercontent.com/assets/2916945/4103570/101d88d4-3168-11e4-937c-5228b3e29be3.png)

Which will result in:

![screen shot 2014-08-31 at 6 40 24 pm](https://cloud.githubusercontent.com/assets/2916945/4103575/3614f914-3168-11e4-822c-92ef88352e53.png)