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/components/channel_header.jsx

@@ -581,9 +581,9 @@ export default class ChannelHeader extends React.Component {
                                         ref='headerOverlay'
                                     >
                                         <div
-                                            onClick={TextFormatting.handleClick}
+                                            onClick={Utils.handleFormattedTextClick}
                                             className='description'
-                                            dangerouslySetInnerHTML={{__html: TextFormatting.formatText(channel.header, {singleline: true, mentionHighlight: false})}}
+                                            dangerouslySetInnerHTML={{__html: TextFormatting.formatText(channel.header, {singleline: true, mentionHighlight: false, siteURL: Utils.getSiteURL()})}}
                                         />
                                     </OverlayTrigger>
                                 </div>