Update VE core submodule to master (b9598c6)

New changes:
0612b31 Allow style attributes to be pasted from other VE instances
aa02be3 Add 'forClipboard' mode to converter

Change-Id: I525584f06be4c13db0373d6d6e94a8f532a888fe
Merge "Update VE core submodule to master (b9598c6)"