This commit raises the minimum supported version of Thymeleaf to
3.0.x. It also upgrades Spring Social to a version that is compatible
with Thymeleaf 3.
Closes gh-7450
Closes gh-6258
See gh-7885
Before this change if Layout dialect not available then the nested class is
loaded and barfs because it depended on the layout dialect (in a
@ConditionalOnClass annotation).