Bug 828751 - Remove innerHTML calls in contacts application

This is a proposed fix for [#828751](https://bugzilla.mozilla.org/show_bug.cgi?id=828751). Removal of all `innerHTML` calls within the contacts app.

Open for debate: clearing elements happens through `innerHTML = ''`, I've changed it to do this via DOM. Perhaps gaia already has taken a stand on that. For that sake I have most of those changes in a separate commit, so please first review before I squash everything into one single commit.