Initialisation

Before a plugin can be used the following happens, courtesy of the plugin manager. But each step only happens once per plugin.

1. If it was added by class then a new instance is constructed using its default constructor.
2. The plugin is initialised via its init() method, which returns a success flag.

If either step fails then the plugin manager removes the plugin and it is not used again.

It is worth stressing that initialisation happens no more than once per plugin. This is regardless of how many interfaces and jobs it has.