This widget is a combo box allowing to choose between three 
possible options to set the time steps.
 
- The first one is a constant time step throughout the calculation.
-  The second one corresponds to an automatic time step based on temperature change observed from time step n-1 to n. It turns out to be very convenient when dealing with very long transient in which source terms or boundary conditions change with respect to time.
-  The last option corresponds to cases where users have an idea of the phenomenon evolution during the transient and want to specify different time steps 
during a certain number of time steps.
________________________
 SYRTHES version   : VERSION_SYRTHES
 Name help file  : comb_time_st.html
 I. Rupp, C. Peniguel  -  may 2014
 ________________________