Fix search description for the G8

Passing in a description field which will be used by the frontend
application without markup
topical events should post desctiption without markdown

for use in search
Fix document series search description
Fix policy group search description
Add organisation description for search
Fix person bio to not use markdown for search
Use summary for corperate info page
strip markup from operational fields for search description
Fix orgs searchable test
Merge pull request #596 from alphagov/g8-summary-fix

Improve the description displayed for search results