Allow its-* plugins to register actions of their own

More and more actions are created in the project. Each one requires
hundred of lines of modifications in its-base. Also most actions will
only be implemented in a unique its-* plugin implementation.

This change allows its-* plugin to expose new actions without requiring
the modification of its-base.

Change-Id: Ib9993cc0643f1524ce31905ebf71e1fe4994c9fa
9 files changed