custom schemes

[antil0l]

very basic implementation of the custom schemes talked in #240, users can call the fetchUserScheme(url) function from console to add their scheme, it gets stored in localStorage so they are gone once you reset the cache, and the scheme gets added amongst the other schemes after a reload of the page with post-fix of -user-scheme. the url domain should allow for CORS for example, the https://raw.githubusercontent.com allows it, so you could upload your schemes to a github repo and get their link from that domain (aka just viewing the raw file will provide you that link).

not very user friendly having to go to console for such thing, but i liked the idea too much.

also fixed a typo from previous PR and some formatting is done on some lines (nothing major).