Scan to check should be case insensitive and ignore URI stuff

[Sjors]

When I scan a BIP 21 QR code it complains that the address is not found in the list.

This is probably because the format is bitcoin:BC1Q...?label=blah

When parsing an address, I suggest the following:

1. check if it contains only alphanumeric characters: process as now
2. parse it as a URI and obtain only the main part of it. Ideally use something like NSURL for this, rather than "manually" processing it, since that's safer.