ISIS-478,ISIS-503: various fixes.

ISIS_478, for conditional choices, for EntitySelect:
* clear link now should work
* if no choices/autocomplete then doesn't NPE (BankMandates#newBankMandate)
* removed ID_ENTITY_TITLE_NULL label, since never visible
* sets up a placeholder text
for conditional choices, for ValueSelect:
* correctly initializes second dropdown based

ISIS-503, for contributee actions/associations, calculate identifier
* was causing stack trace when go back to list, caused by call to getIdentifier() incorrectly returning the wrong value for a contributed association.
ISIS-74: removed BoundedFacet

instead, @Bounded implies a ChoicesFacet on the type, from which are derived
PropertyChoicesFacet or ActionParameterChoicesFacet (same as handling of
enums).

Also removed use of deprecated Filter interface in ToDoItem, using guava
Predicate instead.
ISIS-473: actions now need to be explicitly annotated as @Bookmarkable

(they must also have safe semantics, as previously).
Merge remote-tracking branch 'upstream/master'