Add Graceful shutdown for Windows and hooks for shutdown of goroutines (#8964)

* Graceful Shutdown for windows and others

Restructures modules/graceful, adding shutdown for windows, removing and
replacing the old minwinsvc code.

Creates a new waitGroup - terminate which allows for goroutines to
finish up after the shutdown of the servers.

Shutdown and terminate hooks are added for goroutines.

* Remove unused functions - these can be added in a different PR

* Add startup timeout functionality

* Document STARTUP_TIMEOUT

models/repo_indexer.go

@@ -84,7 +84,7 @@ func InitRepoIndexer() {
 	if setting.Indexer.StartupTimeout > 0 {
 		go func() {
 			timeout := setting.Indexer.StartupTimeout
-			if graceful.IsChild && setting.GracefulHammerTime > 0 {
+			if graceful.Manager.IsChild() && setting.GracefulHammerTime > 0 {
 				timeout += setting.GracefulHammerTime
 			}
 			select {