Restructure Android Documentation

[breautek]

This issue is to keep track of a more complete documentation restructure that should be done after the PRs https://github.com/apache/cordova-android/pull/764 & https://github.com/apache/cordova-docs/pull/1009 is merged.

This is because the Android app bundling feature adds some new build.json features that isn't exactly related to signing, but the current build.json documentation is documented under Signing the app

The new structure at a high level should be as follows:

building the app

[details/information on building the app]

Using build.json

[shows table flags related to build options]

signing the app

[details/information on signing the app]

Using build.json

[shows table flags related to signing options...]

The original discussion can be found at https://github.com/apache/cordova-docs/pull/1009#issuecomment-512227371 and the mailing list discussion can be found here