[WFLY-3556] Timer persistence and restore
Core split: Remove all non-core modules, add dependencies on org.wildfly.core artifacts
Merge pull request #6467 from stuartwdouglas/master

Core split: Remove all non-core modules, add dependencies on org.wildfly...
Merge pull request #6457 from langfr/WFLY-3556

[WFLY-3556] Timer persistence and restore
Improve DIST_ASYNC compatibility by using FORCE_SYNCHRONOUS flag where cache write result is required.
Proactively validate that session attributes are Serializable.