Allow a message with more than one event to be destroyed.

Fixes #1569
Handle converting empty RTF files

Fixes https://github.com/mysociety/alaveteli/issues/1563
Merge branch 'hotfix/0.18.0.2'
Merge remote-tracking branch 'origin/hotfix/0.18.0.3'
Use new status icon names (with old icons)

Defining the basic css for status icons here so that themes can just set
colours and add their own icons.
Copy Brazilian Portugese to Portugal Portugese
Latest translations from Transifex.
Add upgrade notes for anti-spam honeypot
Merge pull request #1 from mysociety/master

Master