Fix #748: Default formatter context to column definition object
Fix #734: Keyboard: do not set tab index on header when it is hidden
CHANGES.md: Note Keyboard header navigation fix
Fix #704: editor: stop eating mousedown events

The mousedown event listener in `showEditor` was interfering with
`selectOnClick` for any TextBox based widget, and it does not appear to be
necessary anymore.
CHANGES.md: Note removal of editor mousedown handler
editor: Fix edge case regression from focus preservation fix
Fix #716: Allow column className to be a function

* A column's `className` property may now be a function or a string. If
  it's a function, it will be called when the row cells are created and
  passed the object being rendered in that row.
* Cells will always include the dgrid-generated "field-<field name>" class as
  long as the column has a field, even if a custom class is also specified.
Add Intern tests for column.className
CHANGES.md: Note support for column.className as function
ColumnSet: fix support for column.className as a function and add tests
Fix #752: Pagination: Ensure numeric rowsPerPage when using drop-down
Fix #755: ColumnHider: Prevent menu from immediately reopening
Update version for tag
Update version for dev towards next release