Add bootstrap-like javascript helpers

[virtuald]

Ideally, should be able to assign a class and a data attribute indicating the NetworkTables key, and the HTML object will transmit/respond based on NetworkTables events. For example, something like a toggle button:

<button data-nt="/SmartDashboard/foo" data-type="toggle" />

.. or something like this. A lot of the UI elements should be buildable without requiring any explicit javascript, to make it simpler to add/extend the UI.

[virtuald]

Another useful control would be a slider, such as @amorygalili has for the websim.

[virtuald]

The TableViewer app (see #10) could utilize these automatically.