Fork ODK Collect instead of trying to use it as a library.

We've been trying to use Collect as a library, but it's not designed for it, and that's causing a lot of problems for us. This branch makes our app a fork of Collect instead, which makes a few things easier:

* Our build system will be less complicated. We should have far fewer problems with dependencies and class loading errors.
* We will have much more freedom to modify Collect classes, since the ability to merge from upstream will no longer be a priority.
* It will be significantly easier to deal with our data. Even if we try to use ODK as a library, we'll either have to make substantial changes to ODK's databases and content providers or use some ugly workarounds.

Our app has a different purpose than Collect, so we're going to make a lot of changes whether we fork or not. If we fork we'll be giving up the ability to easily merge from or to upstream, but I think it's worth it. I think our current approach is going to turn out pretty clumsy and ugly.

What do you guys think?