Guess common repo suffixes when adding repo (Fixes #5)
Any feedback on the UI/UX of this change, a test (I've tested on my 2.3 and 5.0 device with success), or a code review is always welcome.
The idea is that you should be able to type in a single url, e.g. "https://www.myhost.com", and F-Droid should be able to guess that there is a repo at "https://www.myhost.com/fdroid/repo". This change implements that. It had to do a dodgey hack or two in order to show feedback using the same dialog that the user clicked the "Add" button for - but these are documented in comments where suitable.