* Get rid of ugly statik
go1.16 introduced the embed package, it's the more graceful solution for embedding file into binary.
https://golang.org/pkg/embed/
* remove statik totally
* split go and static files in assets
token is the current token comparison, and oidc generates oidc token using client-credentials flow. in addition - add ping verification using the same method
The ServerCommonConf is now passed around as an argument instead of
being shared between components as a global variable. This allows for
more natural interaction with server.Session as a library and allows for
multiple servers to co-exist within the same process.
Related: #1387
1. if client is offline, server will release all resources
2. use a graceful method to shutdown go net.Listeners
3. add closeFlag for Conn, so startHeartBeat func can exit correctly now