Fixes for the omero.properties parser

This PR adds various fixes to the parsing of the `omero.properties` files

- fixes  `bin/omero config parser --keys` broken by the addition of `Ice.xxx` (unless we want it to appear)
- fixes multi-line parsing, e.g. `omero.search.excludes/includes` with unit tests
- fixes indentation for choice lists when exporting to RST
- fixes URLs exposed in the generated RST by moving them to the headers
- ports some `omero.security.*` definitions from the documentation

To check this PR, check in particular the merge auto-generated configuration page for the OMERO documentation.