Consolidate webui folder

[jcvernaleo]

As @jolan pointed out in #1 there are some ways to include the contents of the webui folder in the binary (and then it could write the files to ~/.dcrticketbuyer/webui/).

Including assets in source code is yucky but so is depending on a folder in a known place.

So we should at least consider this (or if there are other options think about them).

[davecgh]

I don't find including the web server assets in the binary bad at all. In fact, I prefer it.