LanguageCategoryDisplay: cache last items instead of finding them repeatedly

addToRegion() and getColumn() would call jQuery's find() up to three
times per execution - and they're being executed a few hundred times
in a tight loop.

Since the finds were used simply to find the last inserted elements
we can just cache them in this's properties.

In my profiling on Opera on a Thinkpad T60 (with lazy-loading
disabled), JavaScript evaluation during the rendering of the dialog is
down from ~880ms to ~450 ms.
Remove lazyload functionality entirely

It was merely a stopgap solution to the problem of the dialog taking
forever to load. With that problem solved all of this awful code is no
longer needed.