Add minimal support to the WordCamp Base theme to allow CSS overrides to be fully responsive

[r3df]

To create a fully responsive CSS override for WordCamp Base, a bit of JavaScript is needed to create an open/close toggle for a responsive menu that is touch screen friendly. Ideally an HTML element for the the toggle button is also needed.

This patch takes the approach from twentytwelve and adapts it to WordCamp Base. The file navigation.js is copied from twentytwelve and adjusted for the different tags in the HTML in WordCamp Base.

An H3 element is added above the menu, as it is in twentytwelve. The element is hidden by default by CSS.

The patch does not yet include all the language file updates for the word "Menu" that has been added.

[r3df]

#357 was marked as a duplicate.

[iandunn]

In 412:

WordCamp Base: Add support for responsive menus. props r3df. Fixes #358.

This does include the CSS rules to show the responsive menu on smaller devices by default, it just adds the necessary menu element and toggle script so that a WordCamp can use the Custom CSS module to make their site fully responsive.

[iandunn]

Replying to iandunn:

In 412:
This does include the CSS rules to show the responsive menu [...]

That should have said does not include the CSS rules.