nested lens usage refactor (part 1)

[kostmo]

Towards #2265.

This will be a multi-part refactoring, since uiGamestate is accessed in hundreds of places. The more repetition that can be eliminated, the easier it will be to eventually modify the type of the record fields.

In this PR, a few no-op refactorings:

• use a narrower type in many places (e.g. pass UIGameplay rather than AppState as function parameter
• define local aliases for long lens chains
• Use zoom for blocks of operations on deeply nested state