Invalid timestamp when transacting with a bad system clock

[heimindanger]

Avalon will refuse transactions with bad timestamps for the transaction. Some users have bad clocks but shouldn't be blocked from using the UI. Instead, we could look at the timestamp of the previous block and add ~3 secs, and use that for transacting on PCs who have unsyncd clocks.

[techcoderx]

Now that we have multisig transactions, we could just use the ts as transaction expiration which can be set to a few minutes into the future to allow some time to gather the required signatures.