Cat API: Improve help and execute help before sending server requests

Just a quick afternoon try to not send the actual requests when you only want to get the help for an endpoint. Still need to take a closer look at the whole API and its design on source code level to be sure, this is the correct approach. @drewr maybe you can have a look...

* Force the cat API classes to have simple help available by extending from a AbstractCatAction
* Use a set binder on guice creation to create the help on node start up
* Make sure that the help/field info is returned without querying any data