This commit was previously split into the following parts to ease
review:
- 2d746f68: replace imports
- 4008f0fd: use ecdsa.Signature
- 849e33d1: remove btcec.S256()
- b8f6ebbd: use v2 library correctly
- fa80bca9: bump go modules
In this commit, we take an initial step towards converting the existing
breach arbiter and utxo nursery logic into contract resolvers by moving
the files as is, into the `contractcourt` pacakge.
This commit is primarily move only, though we had to massage some
interfaces and config names along the way to make things compile and the
tests run properly.
