Use the first two octets of ip addresses in fingerprint()

[xecdev]

Users on dynamic IPs are being logged out each time their public address changes (e.g. home ISPs, cellular, or rotating VPN endpoints). This PR relaxes our fingerprint check in PayButton_State::fingerprint() so that, instead of using the full client IP, we only use the first two octets for IPv4 (e.g. 203.0) or the first two hextets for IPv6 (e.g. 2001:0db8). This will help solve the frequent logout issue and will help the plugin remember a logged-in user's session for a week. I have fully tested this new feature for IPV4.

Test plan:

• Install and activate the plugin
• Use a VPN (which gives you dynamic IP addresses for same location) or release and renew IP through CMD.
• Login via Cashtab
• Change your IP's last one or two octets, and verify that you're still logged in

[Klakurka]

We can try this but much of the time they'll be getting a new ip address that's totally different which tells obviously doesn't address.