Eliminate connection/statement/result set leaks in TableQuery (#10582)

Includes some refactoring to extract common parts of FreeformQuery and
TableQuery to AbstractTransactionalQuery.

svn changeset:25541/svn branch:6.8

Added missing Serializable for AbstractTransactionalQuery (#10582).
    
svn changeset:25559/svn branch:6.8

Conflicts:
	server/src/com/vaadin/data/util/sqlcontainer/query/FreeformQuery.java
	server/src/com/vaadin/data/util/sqlcontainer/query/TableQuery.java

Change-Id: I3d055e0f071739ac4536fddb0f49b8d6b8e6d07b