* also apply live-preview if an unsaved style was disabled
* use box-shadow instead of outline for focus everywhere
* allow focus outline on click in text/search input or textarea
* search inputs should use the same style as text inputs
* also use box-shadow focus on delete buttons
* remove URLSearchParams workaround, not needed since Chrome 55
* use `once` in addEventListener, available since Chrome 55
* update USO bug workarounds, remove obsolete ones
* ping/pong to fix openURL with `message` in FF
* use unprefixed CSS filter, available since Chrome 53
* use unprefixed CSS user-select, available since Chrome 54
* focus tweaks
* also use text query in inline search for Stylus category
* use event.key, available since Chrome 51
Co-authored-by: narcolepticinsomniac
* caching of search results and downloaded style info for one day
* no prefetching of styles
* only the next search results page is prefetched in unattended fashion
* the "configure" button is shown only after installation
* join the code in one closure, regroup and simplify some functions
