#73 Absolute values for column width

[Thierry Excoffier]

Currently columns are displayed with proportionnal width.
On horizontal scroll it is very disturbing.

The column width must not change except for the last one that may be a little smaller or bigger in order to fill the screen space.

With this change, an horizontal scroll column by column will be bearable by the user (actually the fixed columns on the left may change of width each time...)