Move config.xml parsing into its own Config class

Now the parsing happens very early in the bootstrap process, before
loadUrl() is called. This enables a future change to put the start page
in config.xml instead of hardcoding it.
Add configurable start location to config.xml and template

Still possible to hardcode, there's a comment in the template showing
how that can be done.
Added a comment to explain where the start page is getting set.
Merge branch 'master' into start_location