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/orderbook/simulator/simulator_test.go

@@ -1,6 +1,7 @@
 package simulator
 
 import (
+	"context"
 	"testing"
 
 	"github.com/thrasher-corp/gocryptotrader/currency"
@@ -11,7 +12,8 @@ import (
 func TestSimulate(t *testing.T) {
 	b := bitstamp.Bitstamp{}
 	b.SetDefaults()
-	o, err := b.FetchOrderbook(currency.NewPair(currency.BTC, currency.USD), asset.Spot)
+	o, err := b.FetchOrderbook(context.Background(),
+		currency.NewPair(currency.BTC, currency.USD), asset.Spot)
 	if err != nil {
 		t.Error(err)
 	}