(#131) - Bottombar

This is another big commit with some major changes on how we lay things out, but I think it's for the better. It's way more more modular and customizable. The biggest thing to check out is <code>funnel_common.xml</code> which serves as the base layout for all our funnel activities. In this way, we are able to completely handle the previous and next button in the funnel activity since it's standard for every funnel. 

And the bottom bar looks much better. Just call <code>enablePrev</code> or <code>disablePrev</code> to disable the button and put a new image (same works with next of course). Good news too, this PR deleted more code than it added :)