Convert LeakCanary to Kotlin

[pyricau]

1. Update build files to add kotlin support and convert 1 small class to show it wors
2. Convert everything, a few classes at a time. It's important to do small PRs because a.lot of changes could happen at the same time.

[codedsun]

Hey @pyricau , can I know the details for this issue? I am looking to contribute for this!

[pyricau]

@codedsun I'll be spending a hackweek on LeakCanary 2 which will be a somewhat large rewrite, and as part of that I want to introduce Kotlin for new code and later progressively convert the rest of it.

I need to figure out the gradle config changes I need to get kotlin going and then any PR that converts any class is welcome.

Since I'll be working on LeakCanary 2 I have on concerns with backward compatibility of the API, it'll likely all change, including the package.

[codedsun]

No issues! @pyricau . I am little more excited about the hack week you are talking about..Can I also contribute for that or anything else lined up that I can take for now?

[pyricau]

I'm happy to get contributions! Our HackWeek is next week and I'll be focused on that, help welcome!

I started writing the high level in #1211, I'll still need to hash it out to smaller bits / how to organize the work