Pull changes to make installer grab configurl from filename

@aranhoide @myleshorton 

Tested on Mac and Windows.

Right now, it categorically overrides whatever .lantern-configurl.txt was in the user's home folder.  We should think about whether we want to do that, or leave it alone, or be even smarter about it (i.e. if the existing one looks right, leave it alone, otherwise overwrite it).