Configuration setting to allow all users to save powerviews

[danmihaila]

Implement a configuration setting that could allow users to save powerviews. The default behaviour is that only sysadmins can save a powerview

[brew]

PowerView created_by checks against context user:

• Auth for powerview_create (user must be authed for resource) (& tests)
• Auth for powerview_update (user must be authed for resource) (& tests)
• Auth for powerview_delete (& tests)
• Auth for powerview_add_resource (user must be authed for resource) (& tests)
• Auth for powerview_remove_resource (& tests)

[brew]

See commit 15e17f6 for create, update and delete actions.

[brew]

See commit bb8eff5 for add_resource and remove_resource action auth.

[brew]

@danmihaila This is now done!