ISIS-592, ISIS-593: new ViewModelSupport service; change pkg for XmlSnapshotService

Specifically
- updated isis.properties for both services in the example apps (for the archetypes)
- remove dummy action from ToDoItem, accidentally left in
- new ViewModelSupport service in applib and corresponding
  ViewModelSupportDefault impl in oai.core.runtime
- XmlSnapshotServiceDefault moved
  from oai.core.runtime.snapshot
  to oai.core.runtime.services.xmlsnapshot
-
ISIS-594,ISIS-589: simplified URLs; method rename for CSS bundling

Specifically, for ISIS-594:
- IsisWicketApplication, mount pages using mount(...) method
- PageParameterNames, removed ACTION_MODE, PAGE_TITLE, PAGE_TYPE
- BookmarkableModel (as implemented by ActionModel and EntityModel)
  - extended to define getTitle() - since no longer in PageParameters
  - no longer caches page parameters, since caching of title done in subclasses
    - rename asPageParameters() to getPageParameters(), made abstract
- ActionModel now infers pageType, actionMode, pageTitle (caches title);
  also the page parameter's Oid when called in getPageParameters() - as used for bookmarks -
  no longer holds the version (there's no need for bookmarks);
  also creates with INLINE vs REDIRECT mode (since bookmarkable actions have safe action semantics)
- EntityModel now infers pageType, pageTitle
- BookmarkTreeNode refactored significantly:
  - holds bookmarkableModel as field rather than pageParameters
  - infers pageType from runtime type of provided BookmarkableModel
  - now caches title, updateable on matching as previously
  - does matching simply on pageParameters (was able to remove the hack
    whereby pageTitle in page parameters had to be temporarily removed,
    since that is no longer a parameter name at all)
- BookmarkTreeNodeComparator refactored a little:
  - order by pageType (as previously), then class name (for both actions as well as entities), then the title
- BookmarkedPagesModel simplified
  - removed isValidParameters() check, since those parameter names (page title, page type) have now gone
  - #titleFrom helper also removed, no longer called
- BookmarkedPagesPanel now gets page type and page title from the BookmarkedPagesModel,
  rather than the page parameters
- ActionLinkPanel, AppActionsCssMenuLinkFactory updated w.r.t getPageParameters() call etc
- PageAbstract constructor now takes a title, since no longer passed as a page parameter
  - EntityPage and ActionPage provide a title
  - remaining do not, defaults to application name

for ISIS-589:
- renamed ComponentFactory#getCssResourceReferences to #getCssResourceReference,
  because only ever returns a single object
  (in an earlier version of the impl, this method returned a list)
- removed CollectionContentsAsSummary from bundle, trying to get its CSS image url to work
ISIS-594: added guard into BookmarkedPagesPanel

- if an object has been deleted.

This is a temporary workaround for a potential infinite redirect loop
that was observed, though difficult to reproduce.  Try:
a. install fixtures, return first
b. delete first
c. refresh page (in browser)

At any rate, have raised ISIS-596 as a ticket to look at in more depth.
ISIS-593: fixing pom for view model support

- dom4j now a production dependency (previously only test)
ISIS-595: updated BookmarkableAnnotationFacetFactory

as a MetaModelValidatorRefiner, to do the check:
- all @Bookmarkable(As.ROOT) or @Bookmarkable(As.CHILD) must also have
@ActionSemantics(Of.SAFE)
ISIS-595: also fixing example app for simple archetype...

... SimpleObjects#create mistakenly indicated as @Bookmarkable but has
non-safe @ActionSemantics
ISIS-594: fixing wicket sign in page...

... the page title was not being added, meaning could not login :-(