Added a UT_Cache for ObjectPools.

UT_ObjectPoolCache creates a Houdini style cache control for ObjectPools. The plugin creates the default UT_ObjectPoolCache which wraps the ObjectPool::defaultObjectPool() and adds it to Houdini's Cache Manager UI.

Fixes #40.
Passing name in contructor and removed default pool
Merge pull request #85 from andrewkaufman/cacheManager

Added a UT_Cache for ObjectPools