ColumnResizer enhancments

[ghost]

This fixes several issues:

• Adds the ability to mark a column as not resizable (allow for a way to prevent resizing specific columns #325)
• Adds restoring widths by using a width property on a column definition (let ColumnResizer read a width property of a column #321)
• Adds dgrid-columnresize event decorated with the column id and width when the user resizes a column using the mouse (have ColumnResizer extension emit event when a column finishes resizing #320)