Refactor plugin architecture

[Riku Lindblad]

Refactor modules to use decorators more, examples:

• @fnmatch decorator instead of docstring
• @Cron decorator for timed tasks
• figure out a replacement for twisted.python.rebuild (used in rehash)
• http://docs.openstack.org/developer/stevedore/
• https://docs.python.org/3/library/imp.html (imp.load_module and importlib.load_module from py34 onwards)

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