gstlal_inspiral: ranking stat file house cleaning

- correct documentation and add missing documentation for command line options
- --help message is reorganized into conceptual groups
- rework input sanity/safety checking and associated error messages
- make --likelihood-url optional, no file will be written if not supplied, and trigger histogram collection will be skipped for performance improvements
- teak gstlal_inspiral_pipe to not set --likelihood-url options on injection jobs