Add header_action method for panels
Use Capybara to better test panel rendering
Merge pull request #2723 from shekibobo/2552-panel-header-actions

Add header_action method for panels
oops public_send to the view context!
CSV builder: properly deal with non-strings

closes #3130; fixes a regression from #3097
fix tests after 830b0958, 3fb4c514, #3130 :frowning: