Write up best practise to ensure encapsulation

[RealmBot]

Fallout from architectural discussion:

Leaking Internals: In addition to the very flat package structure, many of our classes leak their internals. We have many places where instances return their private copy of a mutable container. Lots of fields are public, mutable, and changed by external code. If this ever bites us, it will be hours in the debugger to find and fix.

GBM will write best practice in Wiki. Keep in mind for new PR/refactors.