Add reporting of loaded plugins

[paulgration]

It'd be useful for Peakaboo to display loaded plugins, plugin version information and potentially other useful information from Galicaster - this is prompting me to think about Galicaster plugin architecture in general..perhaps plugins should inherit from a skeleton abstract/base class (there are no "interfaces" as such in Python) with plugin version info, dependencies and new signals to register etc?

Any thoughts on this?