ENH - Add URL parameter to "Opt" out or "Un-Abandon" all assets

[ChrisBuscaglia]

User feedback - City of New Orleans.

From Eric Ogburn -

Two of the volunteers had difficulty figuring out that 'Abandon' was the correct way to opt out of the system for a particular catch basin. Perhaps highlighting the un-assign option would work. Additionally, adding an unsubscribe button in the emails may be of value.

@JBRaasch