Added data validation to text entry fields.

Text entry fields in GUI now check that data is numerical and within
valid bounds.  Rather large bounds have been set for the moment.
File Open will check that data is numerical but does not validate that
data is within any bounds.
Added status bar display to main GUI.  File Open and Save As will
display status messages.
Right Of Way tab updated so that Update button will ensure table is
pre-populated with valid (albeit not useful) data.