added login buttons and google login

main.py

static/socialSignin/css/buttons-si.css

static/socialSignin/img/bitbucket.svg

static/socialSignin/img/dropbox.svg

static/socialSignin/img/evernote.svg

static/socialSignin/img/facebook.svg

static/socialSignin/img/foursquare.svg

static/socialSignin/img/github.svg

static/socialSignin/img/google.svg

static/socialSignin/img/instagram.svg

static/socialSignin/img/linkedin.svg

static/socialSignin/img/microsoft.svg

static/socialSignin/img/twitter.svg

templates/home.html