Engine/GCTScript: Refactor script manager (#580)

* refactor script manager

* remove singleton GCTScriptConfig
* create constant for ".gct" extension
* move GctScriptManager into vm package
* reduce script manager global dependencies
* use manager struct to store runtime override values
* enable/disable scripting subsystem now doesn't store the setting in
config (aligned with other subsystems)
* setting max VMs via start option doesn't change config

* instantiate scriptmanager as part of creating a new Engine

    * script manager config is now set during instantiation
    * run script manager when enabled in conf or explicitly enabled
    * use the Started() method to check if script manager is running

* in tests set script manager as running

* script manager adjustments

* create manager before attempting overrides
* check for nil config when creating script manager

* fix script manager waitgroup counter increased too late

* move autoload() function to autoload.go
* add tests to script manager

gctscript/modules/gct/common.go

@@ -9,6 +9,7 @@ import (
 	"time"
 
 	objects "github.com/d5/tengo/v2"
+	"github.com/thrasher-corp/gocryptotrader/common"
 	"github.com/thrasher-corp/gocryptotrader/common/file"
 	"github.com/thrasher-corp/gocryptotrader/gctscript/modules/ta/indicators"
 	"github.com/thrasher-corp/gocryptotrader/log"
@@ -79,7 +80,7 @@ func WriteAsCSV(args ...objects.Object) (objects.Object, error) {
 			// a client defined filename and append a date, forces the use of
 			// .csv file extension
 			switch {
-			case filepath.Ext(target) != ".csv" && strings.Contains(target, ".gct"):
+			case filepath.Ext(target) != ".csv" && strings.Contains(target, common.GctExt):
 				target += ".csv"
 			case filepath.Ext(target) == ".csv":
 				s := strings.Split(target, ".")