Replace launchers with App

[rakyll]

Launchers aren't a well established concept in ADK, but an App is.

Following up from changes from #254, consider removing the launcher packages and introduce App.

[yigithankarabulut]

Would it be sufficient to rename Launcher/SubLauncher to App/SubApp, and similarly change the relevant types like uniLauncher/webUILauncher to uniApp/webUIApp?
Or is there a different approach or concept planned for how App will be introduced?

[rakyll]

There is another proposal for an ADK-wide change. We want to align with the broader App concept that will be introduced into ADK.