Add functionality to select multiple Site visits for validation

[helendallas]

At the moment I have to validate each site visit one at a time.

It would be useful to be able to select multiple site visits, after applying a filter such as Owner.

This will save considerable time for admin when it comes to validating data from Owners who have a reliable track record.

[helendallas]

@dimasciput Lets put this on the back burner for now. Other tickets have higher priority thanks