Update and align to latest Springframework project releases

We are currently using three springframework projects: springframework 'core' and the security and mobile projects. For all three newer bugfix releases are available so in principle we should upgrade.
Furthermore, for the content services (sandbox) we're using and extending spring mvc features so aligning with the latest version of Spring is critical.

So far we used the same version for 'core' and security, but these really are separate projects so we need to treat them separately as well, e.g. use their own version property in the main pom.xml.