JBIDE-17455 JBT are not starting when property -Dorg.jboss.tools.vpe.loadxulrunner is set to false

fixed
preview tab reimplemented
fixed some possible NPEs
removed some warnings
JBIDE-17563 Visual part of VPE is blank when JSP page opened

fixed
JBIDE-17455 JBT are not starting when property -Dorg.jboss.tools.vpe.loadxulrunner is set to false

fixed for preview case
move error handling into preview.core plugin
Visual Editor: NPE appeared after editing

fixed
Visual Editor: NPE appeared after editing

fix correction