Fix unknown column width issue

[sourcec0de]

This allows the column definitions to have a default value for their width. I found some difficulties in loading large objects that had an unknown number of fields, so setting their widths

[c0bra]

So this would set the default width of columns to 120 pixels rather than to have each column take up an equal portion of the available space as is the default now?

What happens when (number of columns) x 120px is greater than the grid width? Unavoidable nasty horizontal scrollbar?

[orneryd]

need to come up with a better way to handle this. I'm not going to assign an arbitrary width to the columns by default. By default it should behave like a table and evenly assign the widths.