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

cmd/gctcli/helpers.go

@@ -1,9 +1,13 @@
 package main
 
 import (
+	"context"
+	"fmt"
 	"os"
 	"os/exec"
 	"runtime"
+
+	"google.golang.org/grpc"
 )
 
 func clearScreen() error {
@@ -18,3 +22,13 @@ func clearScreen() error {
 		return cmd.Run()
 	}
 }
+
+func closeConn(conn *grpc.ClientConn, cancel context.CancelFunc) {
+	err := conn.Close()
+	if err != nil {
+		fmt.Println(err)
+	}
+	if cancel != nil {
+		cancel()
+	}
+}