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

fixed the second item in #254: Use GRPC-java instead of HTTP rest which receive the trace segment from agent.

change the grpc protocol

support tomcat  dubbo and httpclient plugins