add eds_pub_date facet

[dnoneill]

closes #1832
needs ebsco/edsapi-ruby#131 to work

[dbranchini]

Screenshots look good. Thank you!

[cbeer]

@dbranchini : are radio buttons the right affordance for this, or would it be better to treat them as regular facet links? With the radio buttons, it seems a little harder to escape from that context and get back to using the date slider (and.. are optional radio buttons even ok?)

[dbranchini]

I'm not sure what you mean by "optional radio buttons"? (I assume they work as a group and you can only select one.) I noticed the radio buttons when Niqui implemented it. I think they're appropriate, but probably better if all of our facets were either radio buttons or checkboxes or none at all. Since I didn't give her much guidance to begin with, initially I thought I'd let it go. BUT this is probably the right time to fix it. Let's go with a standard facet link since that's what we use everywhere else.