Support setting public activity series

User story:

Currently you can make activities public on a per-activity basis, but would be useful to set this on a series. Currently it needs clicking through each one which is time consuming and can be forgotten.

Complexity:

Not so bad, I could have done it when I first added public activities, but left it out to get the feature out the door.

Outcomes (or what needs to be done to move forward):

To be coded!