Better manage pass-through attributes

Hi.  Forgive me if this is all wrong.  I'm new both to git and to Angular (and its supporting technologies).  This old dog is trying to learn some new tricks.  :)

This set of changes allows for attributes on the g+signin element to be passed through to the G+ API.  It tries to be a little intelligent about handling defaults by setting the values that you had in the previous version of this directive, but only if the user hasn't explicitly set a value.

Additionally, I changed the name of the component slightly to make bower happy and revved the component version to 0.0.2.

Please review and incorporate as desired/appropriate.

Thanks,
--Doug