Add ArvadosModel.filter() to support filters API
Avoid extra API lookup to get an object that is already loaded.
Use action_name instead of URI path as the default breadcrumb page name.
Add users/activity page.
Fix up start/end dates and display them in a more friendly way.
Merge branch '2257-inequality-conditions' into 2290-user-activity

Conflicts:
	apps/workbench/app/controllers/users_controller.rb
	apps/workbench/app/models/arvados_base.rb
	apps/workbench/config/routes.rb
Tweak table styles and add Total row
Add link from users#index to users#activity. Not as good as showing it
in the tab itself, but better than no link at all.
Merge branch 'master' into 2290-user-activity
Merge branch '2290-user-activity'

closes #2290