install the four main channels by default, with optional ux channel
beta version bump
update the readme, fix the beta channel

fixing the beta channel reduces the risk that things will be broken when a new beta build is made. this problem doesn't seem to affect other release channel's relying on an aliased 'latest' path.
updated to reflect the recent train switch
Merge pull request #8 from mozilla-boxen/many-release-channels

Many release channels