Search results, various updates for Idea fields

- Add haystack search results in collab format
 - Challenges and Ideas both appear in the same "Ideas" index name
 - Challenges results appear above idea results
 - Ideas sorted by most recent activity date
 - Challenges sorted by most recent start_date
- Add `summary` field - 250 characters 
- change `description` field to `detail`
- all text fields are required (Title, Summary, Detail, Tags)
- challenge drop down only shows active challenges
- Default challenge text is "No challenge"