exchanges: Initial context propagation (#744)

* gct: phase one context awareness pass

* exchanges: context propagation pass

* common/requester: force context requirement

* gctcli/exchanges: linter fix

* rpcserver: fix test using dummy rpc server

* backtester: fix comments

* grpc: add correct cancel and timeout for commands

* rpcserver_test: add comment on dummy server

* common: deprecated SendHTTPGetRequest

* linter: fix

* linter: turn on no context check

* apichecker: fix context linter issue

* binance: use param context

* common: remove checks as this gets executed before main

* common: change mutex to RW as clients can be used by multiple go routines.

* common: remove init and JIT default client. Unexport global variables and add protection.

* common: Add comments

* bithumb: after dinner mints fix

gctscript/vm/vm_test.go

@@ -219,7 +219,7 @@ func TestVMRun(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	err = testVM.Run()
+	err = testVM.RunCtx()
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -444,7 +444,7 @@ func TestVM_CompileInvalid(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	err = testVM.Run()
+	err = testVM.RunCtx()
 	if err == nil {
 		t.Fatal("unexpected result broken script compiled successfully ")
 	}