[JAIEXT-24] Fix bug on the ConcurrentTileCache with multimap

Please look at the following JIRA: https://geosolutions.atlassian.net/browse/JAIEXT-24.

Also a test class for the TileCache has been added. The unused caches have been eliminated.

Guava version has been downgraded to 11.0.1 in order to maintain the compatibility with GeoServer.