Set a timeout for polling performed when queries are evaluated.
* configuration parameters added to control timeouts for queries
* configuration is now propagated to `ClusterContext`
* fixed memory leak caused by `QueryAnswer` listeners never being unregistered

fixes #160
Merge branch 'master' of github.com:ever-been/everBeen

Conflicts:
	been-api/src/main/java/cz/cuni/mff/d3s/been/api/BeenApiImpl.java
	core-cluster/src/main/java/cz/cuni/mff/d3s/been/cluster/context/ClusterContext.java