ISIS-210: choices with param types now also supported.

* changes to ObjectActionParameterContributee subtypes and ActionParameterChoicesFacet to support choices taking parameter types
* refactored to simplify impl of defaults also

in addition:
* updated ToDo example, factored out ToDoItemContributions to demonstrate usage with a new "updateCategory" action
* combined ToDoItemsJdo with ToDoItems service
* new installAndReturnFirst() prototype action

also:
* fixed minor issue with wicket dropdown; the current value must be in the list of choices, else will NPE, so adds automatically
* enhanced rendering of actions to show @DescribedAs as a title
ISIS-499: Add templates for implementing JDO managed relationships as detailed on:
- http://www.datanucleus.org/products/datanucleus/jdo/orm/relationships.html

Includes support for:
- 1:n bidirectional relationship (implemented using a foreign key).
- 1:n bidirectional relationship (implemented using a join table).
- 1:n unidirectional relationship (implemented using a foreign key).
- 1:n unidirectional relationship (implemented using a join table).
- m:n unidirectional & bidirectional relationship (for the entity acting as the parent).
- m:n unidirectional & bidirectional relationship (for the entity acting as the child).

Added also an "iss" template for creating a new Apache Isis section of code between the "// {{" and " // }} " markers. See the "Code Folding" section of the following URL:

https://github.com/danhaywood/apache-isis-ide