Provide preference support

[ctwise]

It would be nice if workflows could have preference panes and define preference items, e.g., "Standard <checkbox>", "Input <drop-down list>", etc.

[jdfwarrior]

This is something that has been brought up in the past and Andrew is aware of it. It's still unclear as to whether or not this feature will make it into Alfred but if it does, I'm pretty sure it won't be for 2.0