Data grid: same overflow wrap on headers and cells.

[fengtan]

Link to relevant issue

This pull request resolves #411

Description of changes

Headers and cells are assigned a different overflow wrap:

• headers have an overflow wrap set to normal here
• cells have it set to anywhere here

As a result headers only break at normal break points (e.g. a space) whereas cells do not. Applying the same overflow wrap to both would resolve the issue.

[hawkticehurst]

Thank you!