Renamed collector, aggregator to api server, api folder to agent (#133)

* Renamed aggregator -> apiServer.

* Format errors with container names.

* Renamed collector -> apiServer.

* Rephrased help messages.

* Moved api -> agent.

* Continue renameing api -> agent in Makefile and Dockerfiles.

agent/pkg/holder/main.go

@@ -0,0 +1,14 @@
+package holder
+
+import "mizuserver/pkg/resolver"
+
+var k8sResolver *resolver.Resolver
+
+func SetResolver(param *resolver.Resolver) {
+	k8sResolver = param
+}
+
+func GetResolver() *resolver.Resolver {
+	return k8sResolver
+}
+