Feature columnautowidth

As described in https://github.com/globexdesigns/doby-grid/issues/98 i added an option "fitColumnsToHeader". If activated:

1.) All Columns will be resized so that the complete content of theire headers is visible
2.) The minWidth of all columns will be set to whatever is larger the initial minWidth or the size of the content in the header.

The result is, that columns cannot be resized to be smaller than their headers content.
I think we need to account for the sort indicator here. Check to see if column has sorting enabled, and if it does - measure the size of the indicator.