Update gradle and kotlin version

[paolorotolo]

Update gradle and kotlin version of the library to allow building with the latest tools.

[davidgyoung]

Thanks for the updates. I am going to have to wait to merge this until I can get it gradle 7 working with the reference app https://github.com/davidgyoung/android-beacon-library-reference-kotlin/tree/wip-upgrade-gradle-7 which is having some build compatibility trouble with gradle 7. I need the build tools to be in sync on both projects because I use it to verify the library functionality when the library is configured as a gradle subproject.

[paolorotolo]

Ah, I did open a pull on the java reference app too: AltBeacon/android-beacon-library-reference#66
I used it to test the new changes with the library submodule.

I didn't notice the Kotlin porting, maybe you could cherry-pick the updates from the java reference pull

[davidgyoung]

Thank you @paolorotolo, I copied in many of your changes to get this working in the branch in a new PR here: #1150, which finally has this working with the reference app.