[hotfix] Add footer slide-in for anonymous users

# Purpose

This PR adds a "slide-in" style popup to the bottom of the OSF, when a non-logged-in user accesses the site.

Closes #1047

The verbiage on the popup has been approved by @saradbowman, as has the functionality.

# Changes

![slidein](https://cloud.githubusercontent.com/assets/131414/5344463/b711f5e0-7edd-11e4-9910-2f9d1794d7bd.gif)

HTML for the slidein was added to `base.mako`, but only if no user is logged in.

The panel slides in three seconds after the page loads. If the user dismisses the panel, a cookie is set to prevent it from re-occurring for 24 hours.

# Side Effects

The jquery.cookie plugin has bene added to `bower.json`; `bower install` must be rerun when this change is deployed.
+1

On Tue, Dec 9, 2014 at 11:04 AM, Steven Loria <notifications@github.com>
wrote:

> In website/templates/base.mako
> <https://github.com/CenterForOpenScience/osf.io/pull/1372#discussion-diff-21538200>
> :
>
> > @@ -71,6 +71,27 @@
> >          </div><!-- end container -->
> >      </div><!-- end watermarked -->
> >
> > +% if not user_id:
> > +<div id="footerSlideIn">
> > +    <div class="container">
> > +        <div class="row">
> > +            <div class='col-sm-2 hidden-xs'>
> > +                <img class="logo" src="/static/img/circle_logo.png"></img>
> > +            </div>
> > +            <div class='col-sm-10 col-xs-12'>
>
> How about adding a close button as well?
>
> Just add the following under this div:
>
>          <a class="close" href="#">&times;</a>
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/CenterForOpenScience/osf.io/pull/1372/files#r21538200>
> .
>