- added some nullptr checks to SFTPSession, SFTPFile and SFTPDir

- now returning pointers instead of objects when creating new SFTPSession, SFTPFile and SFTPDir objects
- removed some debug messages
- changed example program to use the new methods (dir example now works -- no more crashing)

- removed APTEnsWidget and APTEnsDataModel from the example (not relevant to it and previously moved to another project)
- more changes to support SFTPFile and SFTPDir usage
- added functionality to GUI to demonstrate SFTPFile and SFTPDir usage (although the latter is not yet working)

- need to finish implementation and separate into new source and header files

#1. Initial implementation of Session and Channel classes for separation of session and execution channels to support multi-threaded environment.

- added stub file and help menus

- added double and unsigned validation for line edit controls
- added open file dialogs for meteorology and disp phys ensemble files

- now using enum classes and static maps (enum item -> string) for combobox options

- put yield ensemble and HOB ensemble side-by-side
- made soil type and fission id combo boxes with preset lists
- populated data model with initial values and started reading from it while building GUI

- variable name changes

- SessionWorker::requestExec() now also reads and returns from stderr stream

 . in particular, this prevents "qsub" with no parameters which waits indefinitely on stdin
- added parsing for some SGE outputs (submitJob, checkJobs, deleteJobs)

- implemented/tweaked several SGE commands
- added several controls to test GUI for handling new commands and switching schedulers

- changed executables and/or arguments for queue commands based on some quick testing for both PBS and SGE

- changed QueueBase methods to pure virtual

initial check-in of some queue API calls (currently avoiding some linker issues so organization of code will likely change)