FavoriteListViewController: Improve the search bar behaviours

This merge request brings several improvements to the Favorites' search bar with:

• The text field that is now emptied when the user presses the "Cancel" button
• The table view's content insets that are now properly setup in order to avoid any extra padding that is not necessary
• The search bar that is now properly handled when the view is scrolled:
  • The search is hidden when the text field is empty
  • The search bar remains on the screen if the user is currently searching

This merge request also brings a few cosmetics changes with:

• The VLCFavoriteListViewController file's layout that is rearranged
• The VLCFavoriteListViewController files that drop the "VLC" prefix to conform to the Swift standards
• The removal of an unnecessary extension

Search bar - Before

Search_bar_-_before

Search bar - After

Search_bar_-_after