bridge 去中心化跨链桥

每个公链部署一个跨链桥，以及对于的跨链资产合约。

跨链流程

Name		Name	Last commit message	Last commit date
Latest commit History 229 Commits
background		background
bridge-admin		bridge-admin
client		client
contracts		contracts
docs		docs
event-watcher		event-watcher
frontend		frontend
.gitignore		.gitignore
README.md		README.md