Subsystem to enable configuration of Elytron within WildFly

Subsystem currently require patched version of wildfly-core from incubator (branch remoting5_integration), which require patched version of undertow (branch elytron_integration).

After their compilation using mvn install it is possible to install this subsystem into compiled wildfly-core:

mvn clean install -Pinstall2wildfly-core -Dwildfly.core.home=/my/path/wildfly-core/dist/target/wildfly-core-3.0.0.Alpha8-SNAPSHOT

Then you can start wildfly-core using its standalone.sh. Extension and blank subsystem /subsystem=elytron will be already added.

When adding new capabilities add them to Capabilities And Requirements document, please.