fix issue that server list never updated

fix issue that project cycle dependency

Add links of contributors list.

Optimize the plug-in load hints

support test case

Add RefType for ref

Merge branch 'feature/high-performance-agent' of https://github.com/wu-sheng/sky-walking into feature/high-performance-agent

* 'feature/high-performance-agent' of https://github.com/wu-sheng/sky-walking:
  support new api for activation project and fix test case compile fail

# Conflicts:
#	apm-sniffer/apm-agent-core/src/main/java/org/skywalking/apm/agent/core/jvm/JVMService.java

support new api for activation project and fix test case compile fail

Add heartbeat service in InstanceDiscoveryService

add registerTime in ApplicationInstanceMapping because of the register recover service need the origin register time

Feature/254

support new api for each plugin