fix server error on bad entity/question to give 404
Fix #286: filter multi-word tags correctly

Filter by tag name rather than slug, because in the slug whitespace is replaced
by hyphens.
Shorten message that was flowing to the next line
Merge pull request #299 from danielhers/fix-translations

Shorten message that was flowing to the next line
Merge pull request #298 from danielhers/tags-filtering

Fix #286: filter multi-word tags correctly