Smaller homepage: admin trials load only when on

The homepage's admin-only design trials (/?try=lines, type and synth) keep their styles in their own stylesheet, which the homepage includes only while a trial is on. The ordinary homepage, and the pricing, changelog and stats pages that share its stylesheet, are about 29 KB smaller. The cable animation builds the synth cables' extra parts only in the synth trial, so it no longer creates and updates hidden elements on every view. Three synth rules that were not scoped to the trial now are.