Update VE core submodule to master (8280da5)

New changes:
fdbbad7 Followup 2fcc4c0: fix bugs with selection-only polling
d821f07 Getting rid of ve.splitClusters in VE core
efa6933 Add Sucheta to AUTHORS.txt
abd9023 Move Bartosz to principal authors section

Change-Id: I3ff7bd7b48f92e7b01df5589f9f92e15c0a49a08