Update VE core submodule to master (a942301)

New changes:
2cc219a Update OOjs UI to v0.1.0-pre (571f26d0ab)
3543cb7 Protect against offset=-1 in insertContent()
7a3d456 [BREAKING CHANGE] Move selection restrictions from tools to commands
3d847bb Disable desktop context on table selections
41282dd Missed function rename from RangeFix change
dd6c8b8 Support toDomElements returning an empty array
9be6464 Placholder -> placeholder
9bdd0a8 Restore basic styling to toolbar in core target (only)

Local changes:
Move selection restrictions from tools to commands

Change-Id: I88f3d04946bd1d03ed001d747475a8b495a0f64c