Update certificates simply

Fixes https://github.com/theodi/shared/issues/245

This basically adds a link to update an expired certificate to the user's dashboard and the certificate itself.

I'm also going to add some changes to fix #795 too
This might be unsafe; better to set the html_safe on the content going into the flash, not on everything when it's rendered. Something could be injected. Having said that though, I'm not 100% sure that the html safety will make it through the flash storage in the session, so hm.