Reorganization

Lots of reorganization.

Common has been completely removed
common/log has been moved to logger
common/crypto has been moved to siacrypto
common/erasure has been moved to erasure
EncodeRing and RecoverSector has been moved to quorum
longhair has been moved to erasure
messaging.go moved to package network
zeronetwork renamed to debugnetwork
siacrypto refactored
overall improvement of documentation