Implement preferences

[mdippery]

When the application is launched by holding down the ⌥ key, the user should be able to set two preferences:

1. Whether to launch automatically at login or not;
2. The keystroke that activates the screen saver.

[mdippery]

In light of #3, Item 1 is not necessary to implement as part of this ticket.

[mdippery]

In fact, I'm going to close this. I suppose while I'm updating the app, I might as well do it right. The way it works now is pretty cumbersome.

[mdippery]

I'm not sure why this was closed. It seems viable to do for a v1.0 release.

[mdippery]

Keystroke preferences have been implemented, but login item preference does not yet work.