Add tea open (#101)

Fix open default to home page

Improve path join and open with no arg

add labels and milestones

Add tea open

Reviewed-on: https://gitea.com/gitea/tea/pulls/101
Reviewed-by: 6543 <6543@noreply.gitea.io>
Reviewed-by: John Olheiser <john.olheiser@gmail.com>

main.go

@@ -42,6 +42,7 @@ func main() {
 		&cmd.CmdRepos,
 		&cmd.CmdLabels,
 		&cmd.CmdTrackedTimes,
+		&cmd.CmdOpen,
 	}
 	app.EnableBashCompletion = true
 	err := app.Run(os.Args)