Curb Zone availability with restrictions

[jlarsonOmahaNE]

Currently a Curb Zone has an availability_time but not a value for if the zone is actually available. Although this is done at the space level, a new available field on the Curb Zone would allow for the full zone to be closed instead of having to update a close each individual curb space.

I also think that a Restrictions field (with enumerated types) should be added to the curb zone and space where producers can provide information on why the zone is fully closed or spaces have a restriction (such as no stopping; tow zone). The activities could then be redefined that would make them better suited for use.

@zanebclark @schnuerle What do you think?