Aggressive account checking and early reconnect with a 1.5 ^ n retry

This is an experimental patch. I'm sharing it because I'd need verification by multiple persons that it either works or that it has flaws. Do not pull it before we got feedback.

This patch adds a time_tick listener and externalize the account connect/reconnect loop into a "checkAccounts" function.

XMPPConnection gets a retryCounter which symbolizes the retry interval.

I've successfully switched from wifi to gsm and the logic kicked in and reconnected me. I've no idea how well it will work "on the go".