[Proposal] Change the app_resources/android folder structure to meet Gradle specifics

[atanasovg]

[As per @Plamen5kov's comment ]

It might be a good idea to follow the gradle project structure to avoid complicated logic on CLI side when copying resources. This will also help with declaring and controlling xml files, that are currently not the subject of change. Currently, because of the style.xml file we can't build with lower api level than 21. Example of these files:

everything in:
platforms/android/src/main/res/values
platforms/android/src/main/res/values-21

[Plamen5kov]

closing in favour of #700