WIP: Use @Parameter injection

This is now possible thanks to scijava-common 1.9.0, and is cleaner
than grabbing services haphazardly using Context#getService(Class).

It also exposes bugs earlier by ensuring that required services really
are present at the time of context injection, rather than waiting until
the services are actually needed then failing with NullPointerException.
StreamHandle: only set non-null context

If the given context is null, just don't set it. And something else
will need to set the context after construction, in that case.
AbstractReaderFilter: remove obsolete javadoc
Filter: do not implement redundant interface