ISIS-349, ISIS-350: jgrowl integration, error page for exceptions

implemented.
ISIS-349, 350: further improvements

* rendering of the error page is prettier
* had forgotten to remove debug buttons at bottom of PageAbstract
* force JQuery to always be loaded
* inline JGrowlBehaviour instead into PageAbstract
* enhanced ToDo app to demonstrate this stuff.
ISIS-349: removing JGrowlBehaviour from imports.
ISIS-351: services in applib, redirect to error page

* added ExceptionRecognizer interface in applib, along with various helper implementations
* enhanced ServicesInjector (in core) to support multiple services of given type
* enhanced Wicket's ErrorPage to also render simple messages (ie suppress stacktrace for recognized exceptions)
* hooked WebRequestCycleForIsis to look for ExceptionRecognizers and redirect to ErrorPage accordingly
* provided implementations within the JDO object store
* updated ToDo app to demonstrate
* fixed rendering of select2 drop-down choices in Wicket viewer
ISIS-351: now rendering recognized exceptions on action panel

* if the runtime exception is recognized, then will be rendered on the action panel's feedback
  rather than the fallback ErrorPage
* also ensured call abortTransaction if an application exception is thrown.
* moved the threadlocal logic for notifications from ActionModel and into ActionPanel.
ISIS-350: making raised messages persistent across interactions.

* ... by associating MessageBroker with AuthenticationSession rather than IsisTransaction
  (this means in effect moving it from core-runtime to core-metamodel)

also:
* got rid of the hacky thread local for application errors (in Wicket viewer),
  and instead have extended MessageBroker to hold the app error along with the info and warning messages.
* got rid of unnecessary abortTran calls in wicket's ActionPanel
* added missing logging bootstrapping for wicket viewer.
ISIS-351: improving exception handling for no-arg actions
ISIS-352: adding a README.md for github mirror