Add searching of the recommended activities admin page

Test (search functionality)

1. Login as Admin.
2. Go to Site administration > Courses > Recommended activities.
   • make sure there is a search bar in the "Recommended activities" admin settings page.
3. Enter a search query in the search bar that matches a pattern of a name of an existing activity  (ex. "Lesson", "less", "sson", etc.)
4. Submit the search by clicking on the submit button (magnifier icon) .
   1. make sure the entered search query is still displayed in the search bar. 
   2. make sure there is a text label below the search bar that indicates the number of search results found ("Search results: N")
   3. make sure the correct search results (activities) are being displayed in the Activities table
5. Enter a search query in the search bar that does NOT match a pattern of a name of an existing activity  (ex. "Random string", etc.)
6. Submit the search by clicking on the submit button (magnifier icon).
   • make sure there is a text label below the search bar that indicates that 0 search results were found ("Search results: 0")
   • make sure that search results are not being displayed and the Activities table as well.