* section labels, TOC, speedups and fixes
* show section numbers in widgets
* debounce livePreview in usercss editor
* better fixed header and compact layout compatibility
* fix section sizing for compact layout + layout speedup
* DocFuncMapper + cosmetics + fix Clone button
* don't run linter during initSections
* remove unused/unnecessary DOM polyfills
* report invalid @document function as parser error
* rewrite section finder
* simplify focusedViaClick
* simplify setPreprocessor and make it synchronous
* throttle offscreen line widgets in usercss with lots of sections
* add on, off aliases for add/removeEventListener + onOff
* use on/off aliases in changed files
* use getters in more places
* 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
Select text color needs to be specified to override system color in Linux. Also got rid of he stupid dotted line around focused element text which still occurs in Linux FF.
