Add Annotation plugin example

[langsmith]

Annotation Plugin has been released. Demo app needs an example showing how to use it.

[samfader]

https://github.com/mapbox/mapbox-android-demo/issues/995 will get at one part of the Annotation plugin.

[tobrun]

While we added Symbol manager, we can still do some examples around fill, circle and line.

[tobrun]

The annotation plugin lives in this repository. Some existing examples can be found here.

[LukasPaczos]

I think it'd be great to showcase the plugin by adding one example showcasing simple addition of a marker as well as another example that explains differences between data-driven properties and non-data driven properties, multiple managers setup, click/drag listeners etc.