* feat: Using local.properties to provide API key instead of secure.properties.
* Remove redundant declaration in main AndroidManifest.xml
* Migrate ApiDemos - Kotlin to use local.properties.
* Update README for tutorials.
* Genericize.
* Remove references to secure.properties.
* s/master/main
* Update ApiDemos/java to latest Maps SDK for Android
* Update ApiDemos/kotlin to latest Maps SDK for Android
* Update tutorials/CurrentPlaceDetailsOnMap to new Places SDK for Android
* Update tutorials/MapWithMarker to latest Maps SDK for Android
* Update tutorials/Polygons to latest Maps SDK for Android
* Update tutorials/StyledMap to latest Maps SDK for Android
* Update README with better instructions for API key