Leakcanary: Add support for Proguard mapping files

[pyricau]

Leaktraces are hard to follow when the code has been proguarded.

We need the ability to pass a mapping file to the heap analyzer. Not sure how LeakCanary can get that passed in so that it displays the correct when analyzing. We probably also need something that can transform a string leaktrace into an unmapped leaktrace.

Note: Perflib already has support for this proguard mapping files, worth looking at.

[mzgreen]

I started working od this one.