Research Github Template for teal skeleton

[donyunardi]

After a short discussion today with @kumamiao and @gogonzo, we think another alternative to solve the file structure issue is by using GitHub Template. We can create a Teal GitHub Template that users can use when developing teal app. @Polkas already mentioned this early in issue #9 but I am not sure if we explore this further.

If the project structure can be achieved this way, then the addins will only focus on showing available modules and update app.R file.