Use identical visualization for booked and locked commons

[kmohrf]

We currently use similar but distinct visualizations of booked and locked common availabilities. They both use a cross pattern, but the locked entries are a darker shade of gray whereas the booked entries are red-ish:

I’m not sure if that distinction is helpful from a user’s perspective. Either they are able to borrow a common or they’re not, so it might be better to use the same visualization for both.