Renamed "Add" in catalog context menu to "Add layer"
Added check for disposed item before setting image
Updated to final released version of Tycho 0.19
Enabled properties button only when a layer node is selected
Replaced custom generation of stack trace string with Throwable's printStackTrace method
Updated the Sapphire dependencies to have a minimum version of 0.7.0
Added Sapphire feature dependencies (org.eclipse.sapphire.osgi.fragment plugin was missing from builds)