The objective of this pull request is to have one source for content about adding the Android dependency. Before this, there were at least 3 files with repeated the content, inconsistent or used deprecated instructions.

By adding an include _gradle.md, maintenance can be done in one file only and avoids repetitive work in the rest of the documentation.

An include file name _gradle.md was created with the needed content. The file merge the instructions previously contained in:

• quickstart/native/android/_include/_auth0.md
• quickstart/native/android/_include/_api_authz.md

Some edition was made to the content to make it fit between both and modularly in any other file.

In the note used before there was a link to the Github documentation. The link was removed because the documentation source file has the version hardcoded. If the documentation referred is not updated it would be inconsistent with the Maven or JCenter latest version.

A minor note about this is that the block of code was using xml instead of groovy as code block language.

While checking if there was any other repetitive usage of the Android installation explained, the reference in the file libraries/save-and-refresh-tokens.md was found. It was using compile instead of implementation, the first is deprecated. Using the include _gradle.md the file allows keeping the reference updated in a single place.

The included usage was taken literally from the documentation, but in the files is different, so I went with my guts and stick to the guidelines.

I had problems understanding the Wordy instructions for the editor, so my apologies if anything failed on that step, however, it was followed and the editor's corrections were applied.

Update yml files are included.

If this approach please you, I found a similar problem for the manifest, I could take a look later. Please let me know if there is anything else I can help with.

https://docs-content-staging-pr-7900.herokuapp.com/docs/libraries/auth0-android
https://docs-content-staging-pr-7900.herokuapp.com/docs/libraries/auth0-android/save-and-refresh-tokens
https://docs-content-staging-pr-7900.herokuapp.com/docs/quickstart/native/android