Update VE core submodule to master (8ca8c41)

Local changes:
* Rename paste rules to import rules (also used by drag and drop)

New changes:
f5d83f8 Remove data-parsoid removal hack
99f938f Create 'preserveGenerated' mode for cloneElements and use in copy
938b44d [BREAKING CHANGE] Rename paste rules to import rules
c51288c ve.ce.Surface: Move insert HTML path to DM
10ce4cf Provide a FileDropHandler for HTML files
701bb9c Provide a FileDropHandler for CSV and TSV files
ca6b444 build: Update update-oojs.sh and update-oojs-ui.sh scripts

Change-Id: I5cfa15ab3efd03e2c64c2f9f725cb3098f53b32a