This also probably fixes bugs with wrong z-indexing for fresh entities

Entities are only selected after creation if requested - this was
taking a lot of time, and was pointless. The tick-drawing function
doesn't read calculated styles as much now, but it still forces
a reflow when setting the font, weirdly.

Previously, every call to updateSizes() would update every entity. Now, entities
can be marked as dirty, and updateSizes can be called such that it only affects
dirty entities. I changed a few calls to updateSizes to take advantage of this,
but others can probably be optimized too

This was, previously, explicitly handled with a factor of (1 / (1 - x)).
I just regex'd away these factors, so there are probably a few errors.

This reverts commit f99d7b48ff.

Still need to make the divisions more reasonable for larger/smaller values

By default, the world was set to be 1.1 times as tall as the max height
(or the mean). Now, it can be set to an arbitrary factor.

attribution-less characters

Automatic fitting will still move stuff around horizontally.

Having every single property affected by the css transition
meant that switching sources waited for the transition to
complete, and also required for the grabbed class (which
disabled transitions entirely while moving entities). Now,
only height and max-height are affected by the transitions.