* 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
* make usercss editor full-height again
* make sectioned editor open quickly again
* remove leftovers
* autofocus when add/clone button is clicked
* don't fit to content on clicking the add button
* scroll the window to show a manually added section entirely
* autofocus on a manually added applies-to
* disable Save button while loading
* use standard CSS for a focused CodeMirror outline
* trigger refresh sooner by one viewport in advance
* declare refreshOnView as a standard function
* run fixedHeader asynchronously to prevent self-triggering
* account for header in compact mode when fitting to content
* code cosmetics
