Add the possibility to read and display Altitude data
( at 300,500,700,850 hPa)
If there is no 'altitude' data in the current file, nothing visible is changed
If the current file contains altitude data, a choice box is display
near left side of the parameter WIND .
The box give acces at the data available. (10m for the normal
data, 300 or 500 or 700 or 850 ).
If one of the altitude available is chosen, the wind data shown
 in the dialog and the wind overlay are related to this choice. In addition,
a line of extra data is displayed at the bottom sohwing Altitude,
Temperature, and relative humudity
All the 'altitude data are marked by a yellow background
Off course for those wanting to use another units than
hPa,meters and Celsius, it is possible.
Merge pull request #104 from Ptizef/master

Add the possibility to read and display Altitude data