PLT-1752/PLT-3567/PLT-3998 Highlighting links in search, unit tests for autolinking (#3865)

* Added highlighting to links when their URL includes the search term

* Decoupling UserStore from react-router to allow for unit tests involving it

* PLT-3998 Added SiteURL as an option to be passed into the text formatting code

* Removed reference to PreferenceStore and window from TextFormatting

* Refactored TextFormatting to remove remaining browser-only code

* Updated ChannelHeader and MessageWrapper to match the changes to TextFormatting

* Increased max listeners for Preference and Emoji stores

* PLT-3832 Added automated unit tests for autolinking

* PLT-3567 Rerender posts when mention keywords change

* Updated RHS and search to match the changes to TextFormatting

* Broke TextFormatting's dependency on the UserStore

webapp/root.jsx

@@ -16,6 +16,7 @@ import * as I18n from 'i18n/i18n.jsx';
 import 'bootstrap-colorpicker/dist/css/bootstrap-colorpicker.css';
 import 'google-fonts/google-fonts.css';
 import 'sass/styles.scss';
+import 'katex/dist/katex.min.css';
 
 // Import the root of our routing tree
 import rRoot from 'routes/route_root.jsx';