Hardcoded timeout of receive_tx4_sig on server side should be changed

[AdamISZ]

Currently use a not-in-config file cs_single().one_confirm_timeout value for the timeout of the state transition CoinSwapCarol.receive_tx4_sig which is set to 7200 (2 hours) currently.

So there are two things that crop up: 1, in a testing setup with short locktimes, waiting such a long time can end up past various locktimes. 2, this should be an exposed config var probably, even though I am loth to add yet more of them.

Not a blocking issue really, only for testing (probably including testnet, depending on the case).