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

engine/helpers.go

@@ -28,7 +28,6 @@ import (
 	"github.com/thrasher-corp/gocryptotrader/exchanges/orderbook"
 	"github.com/thrasher-corp/gocryptotrader/exchanges/stats"
 	"github.com/thrasher-corp/gocryptotrader/exchanges/ticker"
-	"github.com/thrasher-corp/gocryptotrader/gctscript/vm"
 	"github.com/thrasher-corp/gocryptotrader/log"
 	"github.com/thrasher-corp/gocryptotrader/portfolio"
 )
@@ -131,10 +130,8 @@ func (bot *Engine) SetSubsystem(subsys string, enable bool) error {
 		return dispatch.Stop()
 	case "gctscript":
 		if enable {
-			vm.GCTScriptConfig.Enabled = true
-			return bot.GctScriptManager.Start()
+			return bot.GctScriptManager.Start(&bot.ServicesWG)
 		}
-		vm.GCTScriptConfig.Enabled = false
 		return bot.GctScriptManager.Stop()
 	}