Move alert to templatetag

Ghost User
2018-10-18T15:53:31+02:00

### One-sentence description Move alert to templatetag ### Why? DRY, lots of alerts everywhere we could just easily make it a templatetag. ### Current implementation Lots of alerts, for example ```
{% trans "Your profile has been updated successfully." %} ×
``` ### Desired implementation Put the html in an include and us a templatetag to make this easy to reuse. Could use https://django-bootstrap4.readthedocs.io/en/latest/templatetags.html#bootstrap4.templatetags.bootstrap4.bootstrap_alert, but not sure if we want to rely on this.