Merge branch 'hotfix/0.17.0.2'
Latest translations from Transifex
Remove obsolete require
Merge remote-tracking branch 'origin/release/0.18'
Add responsive assets to precompilation list
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' into wdtk
Merge remote-tracking branch 'origin/hotfix/0.18.0.3' into wdtk