new interface method ObjectCache.getStatistics

the statistics of a cache instance for an application can be retrieved
by calling `app.__app__.getCacheStatistics()`. That's not very useful for the 
default `ObjectCache` but essential for looking into what more complex cache
impls like `SwarmCache` do

we could remove all the other cache statistics methods like `getCacheUsage` 
and output that info in the map returned by `getCacheStatistics()`

i had to bump java to 1.5 for the generics.. if that's a problem we can
remove the generics