CandSession launch now handles bad assessments

* AOManSvc now stores nulls if the (Item|Test)ProcMap can't be
initialised
* CandSessionStarter sets new 'exploded' property on CandSession
if session can't be initialized
* Added support for rendering an exploded session.
A couple of improvements to error rendering
Item/test debug XSLT now runs with empty input doc
Tidied up last changes to CandidateDataServices
Added link to validator in "exploded" XSLT view
Fixes & improvements to resource serving

* "serve file" was serving *source* after earlier changes in this branch
* Removed "session must be open" restriction on accessing author data
* Added "session must be open" restriction to assessment file streaming
Added RuntimeException -> explosion handling

Added code to intercept RuntimeExceptions coming from JQTI+
during item/test processing, and convert them to session explosions.
Removed still-born deleteAssessmentPackage()
Minor tidy to JQTI+ validation

* Removed legacy AbstractValidationResult superclass
* Clarified that validation only generates warning & errors, not infos
Minor tweak to validation output
AssessmentPackage now has richer validation info
Extra validation info now passed to XSLT
Removed validation infos from JSP - no longer used
Clarified message on #times TP runs
Made DSettings application a bit more clever
Fixed "list del settings" JSP

This was not working after moving the 'prompt' field
Del Settings MVC now lets you set TP limit
Used validation info more in instructor JSPs
Candidate summary table updated for recent changes
ZIP report builder now excludes exploded sessions