Add an array of arguments to isReadOnly() method of actions, to let
them change their results depending on what actions are called.
Primarily used by the 'api' action. Ideally in the future that will be
multiple actions. But this might still be useful.
My attempts here are to mimic the `pagination()` method shared by
actions. I'm tentatively adding the `$count` property to actions so that
we can query the number of notices ''being displayed'' per page prior to
calling the actual `pagination()` method itself, since document
relationship `<link>` elements need to be output inside of `showHead()`,
before `showContent()`, which is where `pagination()` is, gets called.
These extra `<link>` elements only appear on pages where pagination
makes sense. They trigger functionality in some user agents, such as
Opera's Navigation Bar for more easily navigating forward and backwards
across a paged set of notices, messages, or group lists, etc.
