Sort up ROS parameters for filter chains

[bjsowa]

Cherry picked from #195

• Explicitly declare all parameters , otherwise get_parameter won't work.
• Remove unused parameters.
• Add read-only flag to all parameters as the filter chains don't support dynamically changing them.

[jonbinney]

LGTM. Setting them all to read only makes sense - if we ever implement updating for them, we can change that.

[jonbinney]

Thanks for this!