inject: implement search-index based search

[myfreeer]

This is not really full-text search, but search over url and title in the search-index.json. The search core should use existing libraries.

• https://github.com/krisk/Fuse
• https://github.com/nextapps-de/flexsearch
• https://github.com/olivernn/lunr.js
• https://github.com/kbrsh/wade
• https://github.com/bevacqua/fuzzysearch
• https://github.com/farzher/fuzzysort

See also #372
Link #179

[myfreeer]

Yari is using fzf.
https://github.com/ajitid/fzf-for-js
https://www.npmjs.com/package/fzf

[myfreeer]

Referring to #785, should make a jsonp-based fallback for file protocol

Or we can just pack the search code and data together in a js, since it should always be static once downloaded.