Add 2 new admin actions (#191)

* Synchronize all gists previews
* Reset Git server hooks for all repositories

internal/ssh/git_ssh.go

@@ -94,7 +94,7 @@ func runGitCommand(ch ssh.Channel, gitCmd string, key string, ip string) error {
 	// updatedAt is updated only if serviceType is receive-pack
 	if verb == "receive-pack" {
 		_ = gist.SetLastActiveNow()
-		_ = gist.UpdatePreviewAndCount()
+		_ = gist.UpdatePreviewAndCount(false)
 	}
 
 	return nil