Update project and add tests.

[IgorGanapolsky]

Update library versions.
Fix gitignore file.

Add Espresso test for RangingActivity.
Lint and refactor RangingActivity.
Format code.

[davidgyoung]

Thanks, @IgorGanapolsky. I appreciate the upgrades.

Two thoughts:

1. I'd like to wait until release versions are available before upgrading to gradle 4.x and gradle tools 3.x

2. The reference application is designed to be as simple of an app as possible that demonstrates the core features of the library. Given this goal, does an espresso test really make sense?

[IgorGanapolsky]

@davidgyoung IMO code coverage makes sense in any app. Otherwise it becomes legacy code, and more difficult to refactor later. Also, the fix of .gitignore as well as Lint corrections make the project easier to maintain and more testable.

What do you think?