Add new search feature

[GhassenRjab]

This PR adds search feature ( related to #552 )

A new search button is added inside an opened board.
On clicking on it, the search sidebar will open and will show the input where to put the search keyword
and the last added ten cards by default.
After typing the keyword, the user has to press enter to start the search.
The matched cards will appear, and by clicking on them, they will open Inside the board.
To make the search as fast as possible, the keyword is matched against the cards' titles and descriptions and only a maximum of ten matches will be shown.

---

This change is 

[therampagerado]

Can we have settings where we can decide in how many cards to search? And also does it search in archived items?

[xet7]

@therampagerado

You can add new feature request as new GitHub issue, and anyone can add pull request with code that adds those features, with possibility of admin to limit results to 10 or any other number of results, and enable searching of archived cards.

But those are not part of original specs at #552 , because returning much more results would really slow down everything when there is thousands of users. This pull request implements those original specs, and for that @GhassenRjab gets all of the bounty for this search feature. @GhassenRjab already spent more time than expected with implementing this feature, it was not easy.