Add default track height preferences

TODO: Simplify to a simple auto-resize with sensible defaults; also affordances for resizing tracks?

### Problem to be solved

In Audacity, we have an "auto-size tracks" preference which automatically resizes tracks from "way too large to be recognizable as waveform" to "way too small to do anything with". Let's tame it a bit:

* When new tracks get added, they're at most 3x the default track height large.
* As more tracks get added, the tracks first start filling out the available vertical space.
* Once the vertical space is full, adding more tracks reduces the size of all tracks proportionally.
* The minimum-height for this feature is the current default track height.

### known bugs from AU3 which may get fixed along the way

https://github.com/audacity/audacity/issues/1743