Documentation enhancements in JCA scheme file

Some parts of the JCA scheme file (docs/schema/wildfly-jca_4_0.xsd) could use some improvements. It's nothing critical, the docs inside are already pretty good.

1, short-running-threads vs. long-running threads - no description for these. What's the difference between the two and why would I want to configure them separately?
2, bootstrap-context - I wasn't able to infer its function based on the descriptions of its attributes, maybe a better description on the bootstrap-contexts element would help.
3, cached-connection-managerType has no description in its child elements.