[las_users] Reload depth selector when switching z-axis

[Bastian Kern <bkern@xxxxxxxxxxxxxxxxx>]

Hi,

I'm using LAS v7 Beta UI and trying to put an switch to the user interface, so 
the user can select to show the model levels or pressure levels on the 
z-axis.

So far I put a constraint in the ui xml file and added an operation, so my 
custom Ferret script for plotting is called.

I like to change the depth selector on the ui, if the constraint is changed 
from "show pressure levels = no" to "show pressure levels = yes", so that the 
depth selector in first case shows model levels (1-90) and in second case 
pressure (0.001 - 1010 hPa). Is there an "easy way" to do that or do I have 
to create an own UI (or extend the existing UI)?