PluginLoader class

[MostAwesomeDude]

Factor out plugin loading and unloading, and general plugin management, to its own class. This is the first part of #7; this factoring has to happen before any alternative interaction with Hamper can be set up.

[mythmon]

This is almost completely unused now, only the CommanderFactor still uses it, and then the change should be trivial. Nix this?

[MostAwesomeDude]

Agreed; patch incoming.

[mythmon]

One small issue I ran into:

(hamper)1@seaborgium> PYTHONPATH=. python scripts/hamper
Loading db from config: sqlite:///hamper.db
Loading command <class 'QuitCommand'>
registered plugin quit as ['baseplugin', 'base_plugin', 'chat']
Loading command <class 'DiceCommand'>
dice setup
registered plugin dice as ['baseplugin', 'base_plugin', 'chat']
Traceback (most recent call last):
  File "scripts/hamper", line 7, in <module>
    main()
  File "/home/mythmon/src/hamper/hamper/commander.py", line 29, in main
    CommanderFactory(config))
  File "/home/mythmon/src/hamper/hamper/commander.py", line 185, in __init__
    self.registerPlugin(plugin)
  File "/home/mythmon/src/hamper/hamper/commander.py", line 200, in registerPlugin
    self.loader.registerPlugin(plugin)
  File "/home/mythmon/src/hamper/hamper/commander.py", line 254, in registerPlugin
    plugin.setup(self)
  File "/home/mythmon/src/hamper/hamper/plugins/bitly.py", line 42, in setup
    self.username = factory.config['bitly']['login']
AttributeError: 'PluginLoader' object has no attribute 'config'

This and the nit I had above are the only issues I see.