Update VE core submodule to master (f5083c6)

New changes:
6ec286e Support for generic file drop handlers
4f2ab66 Generic progress dialog for drag and drop uploads
742e0fe Fix pasteSpecial command
87ea9e9 Fix up/down arrowing off a focusable node
643ea34 spinner.gif: Update with new version from Trevor
ffd8b1e Position the table context relative to the first section node
393776a Fix logic for ignoring (col|row)span=1
f94b10e Don't unmerge spanned cells when spanned cell is removed
3416764 TableContext: Simplify row/column overlays styles
e6c0038 Localisation updates from https://translatewiki.net.
fb1a922 Register select all as a command and perform programmatically
3c1ce93 Make caption tool available when caption selected
dd0ac7d Move disabling logic from tools to commands
8bf33a5 Bold & italic icons for Armenian
058b32c Update OOjs UI to v0.1.0-pre (05f0fefc3f)
c01d115 Create filedrophandlers folder for implementations

Local changes:
* Register new files
* Move disabling logic from tools to commands
  onUpdateState should only ever call setActive. setDisabled should
  already be determined by the command so that it can prevent itself
  being called by triggers.

Change-Id: Icdeaa4c152a0dcd839c8e7cc4e64b2215eb2de1e