Update VE core submodule to master (8eb47c7)

New changes:
7600823 Remove lies about event objects being passed through
4a3adbb Ignore focusin/focusout events on iframes
c5fe1cd Position the paste target just below the top of the screen
71dc684 Reorder CSS rules in ve.ce.Surface.css to make sense
99d3235 Update OOjs UI to v0.1.0-pre (36d0c7dc3b)

Change-Id: I3732683bcd0652b909411beec1dd7a228c2cc6fc