Use ng-bind and ng-bind-html where possible

Switched to using ng-bind and ng-bind-html where possible to make
markup cleaner, more performant, and to permit html or strip html for
content body depending on where it is displayed (list vs view). I’ve
also added a filters.js and ng-sanitize.

To display (say submitted) content with html use
ng-bind-html=“article.content”. Angular.js does strip most all bad
stuff out and only permits things like <p> and <b>.

To display only the text from content and strip out the html use
ng-bind-html=“article.content | htmlToPlaintext”.