Support for drawdown observations; manual editing of PEST control file

[mmamobile 1]

Please consider adding support for drawdown observation data - particularly as it would pertain to parameter estimation simulations.  For MODFLOW-2000/2005/NWT where the observation process is being used, this change would be relatively easy to implement via a change to the ITT flag value.  For MODFLOW-USG, the change may be even easier to implement through an additional call to usgmod2obs that extracts relevant simulated drawdown values.    

It would also be useful to provide an option to pause PEST execution following creation of the input files - the control file, in particular.  

-Mike