Centralize reset/reload utilities, reset image and font caches

Here is a patch for the centralized caches cleanup.
It implements what discussed on the mailing list and refreshes the status page documentation accordinly (btw, the diff does not contain the new status page screenshot)

Patch looks good for the most part. One thing is how the handlers are being invoked from the GeoServerImpl class. I wonder if they should be wrapped in try catch block so that errors from the handlers are not fatal. I know we had this issue with Catalog listeners as well and in the end came up with a special exception that would allow listeners to legitimately throw exceptions, but in other cases like NPE the exceptions are caught and execution continues.

Sure, I can do that. What behaviour do we want then, log at severe level and continue?

Yeah, I would say that makes sense. And if we do feel the need to throw exceptions we can come up with something similar like we did for catalog.

Here we go with an updated patch. Guards the listeners calls and resets the CRS subsystem as well. Tested, it actually forces GeoServer to reload the user provided CRS definitions in user_projections/epsg.properties as well (neat!)

Review-ping

Patch looks great to me.

Fixed on 2.0.x and trunk

Mass closing all issues that have been in "resolved" state for 2 months or more without any feedback or update