Fix batch action regression

Add csv and xls export to example app

Clean up examples

Merge branch 'bugfix/bogus-sort-url-param' of https://github.com/SpotlightKid/flask-admin into handle-stale-sort-parameter

Merge branch 'feature/support-column-props' of https://github.com/iavael/flask-admin into sqla-column-property

Fix #1706

Merge branch 'raise-on-integrity-error-exception' of https://github.com/jmagnusson/flask-admin into raise-on-integrity-error-exception

Fix #1725

Added missing extra arguments to the ViewArgs