create a "Dated" To-Dos tab

Requires https://github.com/HabitRPG/habitrpg-shared/pull/350

This PR adds a "Dated" tab to the To-Dos column, which displays all uncompleted To-Dos that have due dates assigned (both in the future and past). It does NOT sort the To-Dos by date because that's significantly harder. 

Dated To-Dos are ALSO shown in the "Remaining" tab, just as they are now. The "Completed" tab also works just as now (shows all completed To-Dos regardless of whether they have due dates).

Other changes in this PR:
- rename "Remaining" To-Dos tab to "Active" to save space
- rename "Completed" To-Dos tab to "Done" to save space
- allow the form for adding new To-Dos to be visible even when completed To-Dos are being viewed (consistent with other columns)
- make the hide/show code for To-Dos consistent with the code for Dailies and Habits (i.e., use @Gaelan's code from https://github.com/HabitRPG/habitrpg/pull/3574)
- remove some unnecessary commented-out code

I've tested this without finding problems, but the last time I did something like this I broke Challenges...   **Would someone be able to test this locally, or can we put it on beta first?**

![screen shot 2014-11-01 at 9 08 38 pm](https://cloud.githubusercontent.com/assets/1495809/4871476/ef148f9e-61b8-11e4-8566-ca72bc5260f0.png)
![screen shot 2014-11-01 at 9 08 51 pm](https://cloud.githubusercontent.com/assets/1495809/4871477/ef21cc54-61b8-11e4-9322-61cf59b2f517.png)
![screen shot 2014-11-01 at 9 15 20 pm](https://cloud.githubusercontent.com/assets/1495809/4871478/ef24a0f0-61b8-11e4-9bf5-2803d2d5054b.png)