add stale option to couch requests in exports view

http://manage.dimagi.com/default.asp?123161

also replace get_db with model-specific references
make the app by xmlns lookup stale

this is only used in get_custom_response_message
remove unused imports
fix test
Added export to excel in IntraHealth reports
Merge pull request #3848 from dimagi/exports-stale

add stale option to couch requests in exports view
fix incorrect property name
Merge pull request #3852 from dimagi/broken

fix incorrect property name
Merge pull request #3851 from lwyszomi/intrahealth-export

Added export to excel in IntraHealth reports
Merge pull request #3849 from dimagi/stale_custom_response_message

make the app by xmlns lookup stale
Merge pull request #3850 from dimagi/cz

remove unused imports
Merge branch 'master' into case-123236

Conflicts:
	custom/intrahealth/reports/recap_passage_report.py