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
This commit lets the watchtower automatically create hidden services
by giving it a pointer to a TorController. The server was also slightly
refactored so that it was not the sole owner of the TorController.
