* MM-22622 Check mentionHighlightsDisabled in markdown
* MM-22622 Use array of mentions instead of long conditional
* MM-22622 Disable Channel mention highlight for channel header change messages
* MM-22622 Update tests to ensure mention highlight disabled on system message
* MM-12901 Create showSearchModal action and use for hashtags
* MM-12901 Improve handling of hashtags on Recent Mentions, Flagged Posts, and Permalink screens
* MM-10273 Add hashtag support
* Put hashtag search in a proper modal
* Change hashtag search style to match regular search
* Move Hashtag component and explicitly pass props
* Add unit tests for Hashtag component
* Fix merge conflict