Visit Type dropdown change to Activities tag multi-select

## Basic Information
95% of visits will be for dog-walks, none will typically be a "Vet"-specific visit - I'm not sure where this came from?

A volunteer might undertake multiple activities during a visit, so perhaps this field is better re-purposed as an "Activities" tag multi-select (similar to the Contact tags). Suggested initial tags to choose from:
- Walk (pre-selected)
- Transport (volunteers sometimes assist transporting the client or pets to/from locations, one of which might be a vet, groomer, etc)
- Meds (for the pets or client)