Changes messages name to alerts

To differentiate popup messages from error and success alerts, the
alerts naming has been moved to "alerts" instead of "messages"
Adds partials for abbreviation popups

Partials are added to manage introduction of popup divs around
abbreviations.
Adds popup styling

Adds styles to popup box, using WIC as the prototype.
Renames 'messages' to 'popups' and adds popup container
Adds initial JS

Adds initial JavaScript for handling the popups. Also, fixes incorrect
filename for additional popup partials and adds initial structure to
remaining partials.
Adds popup management logic

Adds JavaScript to open and close popups.
Fixes popup closing issue

Fixes issue where popup wasn't closing when term was clicked a second
time.
Merge pull request #103 from codeforamerica/53_clickable_terms

53 clickable terms