This commit factors out the btcd and ltcd options into their own sections
similar to neutrino, and adds a bitcoind section as well. Now, you specify
node options similarly to:
--ltcd.rpchost=...
or
--btcd.rpcuser=...
or
--bitcoind.zmqpath=...
For Bitcoin, you specify an alternate back-end to btcd as follows:
--bitcoin.node=bitcoind
or
--bitcoin.node=neutrino
You can also specify the default option:
--bitcoin.node=btcd
For Litecoin, only `btcd` mode is valid, and corresponds to the `ltcd`
section. For example:
--litecoin.node=btcd
--ltcd.rpchost=...
The new code also attempts to read the correct options and auth info
from bitcoin.conf just as it does from btcd.conf/ltcd.conf.
This commit adds the fee negotiation procedure performed
on channel shutdown. The current algorithm picks an ideal
a fee based on the FeeEstimator and commit weigth, then
accepts the remote's fee if it is at most 50%-200% away
from the ideal. The fee negotiation procedure is similar
both as sender and receiver of the initial shutdown
message, and this commit also make both sides use the
same code path for handling these messages.
