Ensure that all Spring dependencies are 4.0.0.M2

Spring Security brings with it a transitive dependency on spring-jdbc
which, in turn, pulls in spring-tx. This was leading to these two
modules being version 3.2.3.RELEASE whereas the rest of Spring was
version 4.0.0.M2.

An explicit dependency on spring-jdbc has been declared which ensures
that all Spring dependencies are the same version (4.0.0.M2)