Highlighting the area where you are to drop the page (Bug #1377764)

As it's not obvious where exactly you are to drop the page to add it
to a collection as the droppable bit is either the grey 'no pages'
line or the table of existing pages.

Change-Id: I81e3b7339b020d2e3fd5c4671dcba0c049da39d9
Signed-off-by: Robert Lyon <robertl@catalyst.net.nz>
Merge "Highlighting the area where you are to drop the page (Bug #1377764)"