Removed com.extjs.gxt from pom and gwt.xml
also corrected a UIbinder error introduced by prev commit
Added interface definition for the Argument property editor
Beginning to flesh out the structure for argument property editor panels
Merge branch 'gxt3-sandbox' of https://github.com/strootman/de-widgets-module into gxt3-sandbox

Conflicts:
	src/main/java/org/iplantc/core/widgets/client/appWizard/view/fields/properties/ArgumentPropertyEditor.java