cache avatar data

Please come up with a cache for avatars.

I'm tempted to file this as a bug.

Our Jira server crashed today (JSP-78580).
Looking through the stack traces of the thread dump, I see that 102 threads are locked reading the database.
9 of those 102 threads where locked reading avatar data.

This shocked me.
In our system the avatars rarely change - once a year if ever.
10% of our locked threads certainly should not be spent on looking up avatars.
It should be 0%.
If there ever was a candidate for something that needs to be cached, avatars are it.

Looking at the code I see the interface AvatarStore has only one implementation: OfbizAvatarStore
whereas most animals like this have 2 implementations, an Ofbiz* and a Cached*Delegate.

Please come up with a cache for avatars.