Added "Favorites" link to HeaderSessionView.

Added "updateSession" event, fired when favorites change from 0 to 1 or 1 to 0.

Fixed this bug: new tags are not run through slugg client-side (add a tag with a space, see that the space is not replaced with a hyphen until returning to the page).

Added new "votes" property to "Comment" class in populate_database.html (to keep it in sync with changes from this commit: https://github.com/klyngbaek/PluggedIn/commit/187b7b45467d0c972d42a5bc43e222c40595f4db )