SpringBoot Upgrade to Thymeleaf 3.1.0.RC1

We should also remove our dependency to thymeleaf-extras-java8time (and its dependency management) since it's now fully included in the Thymeleaf distribution. See thymeleaf/thymeleaf#912

Comment From: wilkinsona

All being well, there should be an RC of Thymeleaf and the Spring Security Extras module in time for our RC. That shouldn't stop us from upgrading to the latest milestones in the meantime though.

Comment From: danielfernandez

Please note Thymeleaf 3.1.0.RC1 is already in Central.

Comment From: wilkinsona

Thank you, @danielfernandez.