MDL-43089 Improve page linking, repagination and drag and drop of slots

Including the following fixes
fixed reference to repaginate class
get link and unlink page buttons displaying correctly
creating a util.page js class
util-page now loaded correctly in browser
slotnumber+1 makes repaginate work correctly
using latest js page.getId method
remove unused code
use js method util.slot.getNumber for slot number
comment out js link page functionality
reorder slots when slot dragged
reorder slots when slot removed
refactor reorder_slots()