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

exchanges/exchange_test.go

@@ -1,6 +1,7 @@
 package exchange
 
 import (
+	"context"
 	"errors"
 	"net"
 	"net/http"
@@ -2138,7 +2139,7 @@ func TestGetSubscriptions(t *testing.T) {
 
 func TestAuthenticateWebsocket(t *testing.T) {
 	b := Base{}
-	if err := b.AuthenticateWebsocket(); err == nil {
+	if err := b.AuthenticateWebsocket(context.Background()); err == nil {
 		t.Fatal("error cannot be nil")
 	}
 }