Allow using adjustments by name without configs

[doublejosh]

The first implementation of personalized adjustments (#31) requires adding a config to describe selectors and map to user detail properties. You should be able to do this without any configs just by name.

Example

groucho.userSet({'region':'North America'});

<span data-groucho-region="Europe">This is hidden</span>
<span data-groucho-region="North America">This is revealed</span>

If no config exists for that data attribute, then just look for the corresponding user property. Could decide to require all adjustments to be configured once even one is present.

Motivation is for easier adoption of the tool, and avoiding the need for obvious configs.