This commit removes the `Litecoin`, `LtcMode` and `LitecoindMode`
members from the main LND `Config` struct. Since only the bitcoin
blockchain is now supported, this commit also deprecates the
`cfg.Bitcoin.Active` config option.
To allow nodes more control over the amount of time that their funds
will be locked up, we add a MaxLocalCSVDelay option which sets the
maximum csv delay we will accept for all channels. We default to the
existing constant of 10000, and set a sane minimum on this value so that
clients cannot set unreasonably low maximum csv delays which will result
in their node rejecting all channels.
