Improve grib data panel ( Add unit symbols and use all available space for data )

1)  unit symbols : better user information
2) use all available space for data
    The columns number calculation has almost always a result of 6 ( 2 groups of 3 ) thus a part of the space is lost and 1 line more is used
    There is very little possibility to have really 3 * 3 data to display on the same line as only wind , waves and currents have 3 data . So I choose to set arbitrary , the column number at 9 ( 3 groups of 3 ) . All the space is always used and only in few cases the panel is a little longer (see shots "before" and "after" attached
3) correct a little bug in mmHg calculation.
Jean Pierre
![after](https://f.cloud.github.com/assets/2202442/567077/8bc89aae-c6a8-11e2-8097-a973830c546e.jpg)
![before](https://f.cloud.github.com/assets/2202442/567076/81b0ce6a-c6a8-11e2-8312-10e673b458f0.jpg)