Tab and navbar fixes

This changes both the appearance and the logic behind our tabs. I took another stab at these this morning, and I'm much happier with them now. @CakeBrewery, it would be awesome if you could (or could show me how to) create some Protractor test cases that would try to do some navigation between various pages using our tabs and then navigate using the back button to make sure all browsing history is preserved as expected.

As per @Clebeuf's request, we are also now displaying the xs navbar at the top of the page when the user scrolls past our large navbar. 

This also includes **all** the map changes opened in #47, so merging/closing this one will automatically close the other.