WorklogHistoryCacheImpl doesn't remove cache registration on disposal

From JST-4291

It's not possible to disable and re-enable the GH plugin in UPM atm. The problem is that the com.atlassian.greenhopper.service.timetracking.WorklogHistoryCacheImpl doesn't clean up its registered cache on disposal. It should implement org.springframework.beans.factory.DisposableBean and call cacheManager.removeCache(CACHE_NAME) (watch out for ISE) or check for net.sf.ehcache.CacheManager.cacheExists(String) on afterPropertiesSet.