Restructure High Availability Guide

After migration to adoc, the headlines got converted incorrectly, while at this we want to reshuffle this to correspond more with:

1. Introduction To High Availability Services
2. Distributable Web Applications
3. EJB Services
4. Clustering API
5. Singleton deployments
6. Singleton MSC services
7. Infinispan Subsystem
8. JGroups Subsystem
9. Singleton subsystem
10. mod_cluster Subsystem
11. Clustering and Domain Setup Walkthrough