allow for word wrapping in headers while using fitData layout

[agileminor]

Is your feature request related to a problem? Please describe.*
For larger tables, users would like to see as many columns as possible while keeping data readable. In this case, it is often better to word wrap the header text, but not the data.

Describe the solution you'd like
Currently layout fitData includes the header text, which effectively blocks word wrapping. It would be great if Tabulator had either a separate flag for fitData and fitDataAndHeader, or allowed headerWordWrap to override fitData for the column headers.