Rationalize handling of menu actions and contributed actions

Currently we have the following annotations:

• on the domain service: @Hidden - to hide all actions (still in the metamodel); nb: this has been deprecated in ISIS-970 with no replacement
• on the action: @NotContributed to suppress being contributed, optionally @NotContributed(As.ASSOCIATION) or @NotContributed(As.ACTION); is still in menu
• on the action: @NotInServiceMenu to suppress being in menu; can still be contributed.

This is all somewhat clumsy, and the negative @NotXxx annotations are confusing to read (@NotContributed(As.Xxx) in particular).

~~~
In Naked Objects MVC they distinguish between three different "types" of service:

• menu services (actions are on menus and are contributed)
• contributions (actions are only ever contributed)
• system services (actions never appear on menu or are contributed).

This separation works well; "domain-level" system services (typically factories and repositories) are injected into the "view-level" menu or contribution services.
~~~

This ticket proposes:

Extend @DomainService to characterize the nature of each domain (similar to NO MVC):

@DomainService(nature=VIEW | VIEW_MENU | VIEW_CONTRIBUTIONS | DOMAIN )

where:

• VIEW = current behaviour, and the default
• VIEW_MENU = actions are not contributed
• VIEW_CONTRIBUTIONS = in other words actions are not in service menu
• DOMAIN = are not shown in view ie actions implicitly hidden

In addition, extend @ActionLayout to include further UI hints:

@ActionLayout(
    contributedAs    = ACTION|ASSOCIATION|BOTH   // default is "BOTH"; equivalent (inverse of) the current @NotContributed(As.Xxx)
)

which for domain service of VIEW or VIEW_CONTRIBUTIONS can restrict the contribution if required.