No need for a reusable Fragment here, its only used in one place. This
changes the structure to be a regular Activity, with all View and Menu
setup in XML files loaded in onCreate().
This also converts the URL to a TextView. Having it editable in this
Activity makes for a confusing user experience. Instead, the "Add Repo"
input should validate the URL and not allow creating repos that don't work.
This also purges the use of UpdateService.UpdateReceiver, it will be going
away in the upcoming commits.
