Update VE core submodule to master (f4ff1d6)

New changes:
d845991 Data model implementation for tables
a27c148 ContentEditable implementation for tables
3c47428 Actions and context menus for manipulating tables
543ca54 Support annotation tool on table selections
149cf3d Supporting copy paste of single table cells
25c9eee Table header/data format tools
e557e46 Merge cells tool
afcf2d9 Allow custom type and attributes when creating a table

Local changes:
Add the files and messages for table editing

Change-Id: I6e6c33b96d3089049a0fd5385191caa83df5756b