Add app content layout in app_launcher

[nferhat]

Add app_content_layout option to the app_launcher to allow styles such as the following:

Falls back to a vertical layout if the given entry is invalid.

[Kasper24]

@JavaCafe01 I'm planning to remove all these styling options and use templates instead. I don't mind if you wanna merge for the time being though

[javacafe01]

@real-fht closing in favor of #198