[FIX] board: Do not offer to create dashboard when there is no action

In case we have no defined action (e.g. redirection by python code), adding a dashboard should not be possible as the rendering based on the action.
This patch hides the 'Add to Dashboard' button in search view (opw 611288)
Merge branch '7.0' of https://github.com/odoo/odoo into 7.0-win32