User search

- UserRepository
— adjusted the GetAllUsers and GetAllUsersSearch queries to take
keyword, sortBy & sortOrder (& pagerOffset & itemsPerPage)

- header
— search button now changes depending on current page
—— users.php: Find users (—> users.php)
—— all other pages: Find songs (—> index.php)

- pager
— totalPages & totalResults now change depending on current page
—— users.php: allUsers
—— all other pages: allSongs

- index
— replaced '$allResults' with '$allSongs' to prevent confusion between
allResults and allUsers

- users
— itemsPerPage default value is now 5
— 'No users found' message with link to search box
— Display filter equal to index
—— sort by username or by join date, ascending or descending
—— set items per page
—— reset filter
—— included pager (top & bottom)
—— wrapped single user outputs in media <div>
—— added bumbltar & join date to output
CSS clean-up

- Clean-up
— removed '.content' (not necessary)
— styles for user images in users.php