Friendly access denied message pages

When a volunteer is logged in and tries to access a page that requires specific permissions and the volunteer does not have those permissions, we should display a friendly error message page.

We should probably start with a friendly, generic permission denied page for any logged-in volunteer with access denied. We can then tailor that page for specific categories of access and restriction if we want to do that later.

A friendly page should show up when volunteers tries to act in a role they don't have permissions for, and a friendly page should also show when volunteers tried to claim things that a different volunteer has already claimed.