Updated icons and brief change to the way that JxFileDialog works. It
will change dramatically later on, so the changes aren't very important.
For the GUI, a check for nulls was added to avoid NPEs.
Further null checking in the GUI. Also enforced a maximum row length
based on the first row extracted.
Two images added to JxFileDialog, missed in previous commit.
Created SQLServerTable (not ready for use).
Created Credential class to store Database credentials, as well as a GUI
window for data entry and a listener.
Implemented CredentialEntry in ExportListener and GUI.