Enhance theme list speed and code style.
Enhance theme list speed and code style.

themelist is no longer a global.
1 loop on load, the onchange event is instant.

lastorset/rust-playpen,rust-lang/rust-playpen,Enamex/rust-playpen,plietar/pony-playpen,plietar/pony-playpen,Enamex/rust-playpen,chris-morgan/rust-playpen,chris-morgan/rust-playpen,Limvot/kraken-playpen,rust-lang/rust-playpen,chris-morgan/rust-playpen,Limvot/kraken-playpen,Enamex/rust-playpen,rust-lang/rust-playpen,tilpner/rust-playpen,Enamex/rust-playpen,tilpner/rust-playpen,lastorset/rust-playpen,chris-morgan/rust-playpen,lastorset/rust-playpen,plietar/pony-playpen,rust-lang/rust-playpen,plietar/pony-playpen,lastorset/rust-playpen,Limvot/kraken-playpen,tilpner/rust-playpen,tilpner/rust-playpen