Thymeleaf 2.1.2 upgrade and fixes

Thanks for an excellent module.  Here are some changes that we have made:

Fixes:
* Correct compilation of example project (compiler settings copied from module project)
* Correct bootstrap css include to be relative, like other includes in same area
* Correct parent pom to be magnolia 5.2.1 too

Improvements:
* Upgrade Thymeleaf to 2.1.2.RELEASE
* Copy spring model attributes into the spring web context so are then accessible from thymeleaf