LRU cache for in memory dimensions

The dimensions are kept in memory to fill up the result set.

Now as and when more cubes are created, all the dimensions keep accumulating in the memory

This means tomcat memory requirements always keep increasing

It would help if less frequently used dimensions are swapped out to keep memory in check.

We can have a Cache Manager which gets to decide which dimensions are kept in memory and brings in as and when its required. The size of the cache should be tuneable.