Cache size (rebased onto develop)



This is the same as gh-846 but rebased onto develop.

----

 Fix problem described in http://trac.openmicroscopy.org.uk/ome/ticket/10502

To test:
 * Connect, open an image
 * Switch user.
 * Open the image.
 * Check the insight log and make sure you do not have the following entry
```
Cannot retrieve cache with ID: -1java.lang.IllegalStateException: The CacheManager is not alive.
	at net.sf.ehcache.CacheManager.checkStatus(CacheManager.java:831)
	at net.sf.ehcache.CacheManager.getCache(CacheManager.java:506)
	at org.openmicroscopy.shoola.env.cache.CacheServiceImpl.setCacheEntries(CacheServiceImpl.java:263)
```