NFC swap now goes to confirm swap, not manage repos activity.

The NFC message now is handled by the FDroid activity, so it is treated the same way as every other incoming repo URL. Because FDroid handles incoming intents correctly, the NFC one just magically works when the is moved from ManageReposAcivity to FDroid without further code changes.

The other change is that the two way swap only happens when both are actually swapping. Otherwise, we will send a request for someone to swap with us, when we are incapable of swapping with them.

Fixes #267 (closed).