Swap jshint with xo (+2 more small fixes) (#3916)

This includes fixes for the API Builder command search feature,
and a fix for the provider images not showing in /config/providers

Commits:
-----------

* remove jshint and unneeded files

* lint browser.js

* lint parsers.js

* lint ajaxEpSearch.js

* fix conflicts

* lint browser.js and replace arrow with normal function

* lint js, remove old mocha files

* lint rootDirs and remove no-console for now

* lint blackwhite

* lint testRename

* lint configProviders

* lint js files

* switch mocha+jshint to xo for ci

* remove sass from Grunt, use npm test with appveyor

* Fix build

* use longform for objects

* add XO code style badge

* Update comment in editorconfig

* Review changes

* Fix images in config/providers

One forward slash can ruin everyone's day

* Fix apibuilder

* Add scroll to command feature

* Fix lint