gui: Refactor duplicate table models into a common PlowTableModel
gui: Task/Node/Cluster panels refactored to use PlowTableModel subclasses
client: remove some old exception handling for connection errors
gui: More refactoring on PlowTableModel to add common methods
gui: Reduce code in Task and Node Panels by calling common superclass methods
gui: JobProgressBar draws color progress from left to right;
refactor a bit of the data value lookups
gui: New Layer panel added to default Artists workspace
refs #42
gui: Turn off grid lines for Table views
client: fix typo in docs