Set up modal for social media sign up

[#62170702] Made several changes: changed file name to
social-modal.html, added welcome text and different sections for
Facebook, Twitter, and Google. Set up the title to have a span around
the network's name, it is styled to capitalize whichever name is placed
there. There are several blank attributes where angular needs to be
placed, such as "ng-click" "ng-controller" etc.  Please look over and
make those attributes as you need them. @emilioeduardob