Since composer windows are now only created on demand, and
destroyed when the window is closed, the old interface methods
no longer apply. The new interface methods openComposers(),
openComposer(), closeComposer(), composerOpened(),
composerWillBeClosed() and composerClosed() are similar, but
only apply to composer windows when they are exist (i.e.
are currently open).
To access all compositions from a project, the project's
layoutManager() should be used instead.
Additionally, the new interface methods work with
QgsComposerInterface objects instead of QgsComposerView
objects. This should allow future hooks for plugins to interact
with open composer windows in a more useful way.
Not much there yet, but it adds an interface with stable API
which can be used by plugins and scripts to interact with
composer windows.
Could be expanded in future to add hooks for toolbars, menus,
etc, allowing plugins to extend composer functionality.
