add hook EditorAction::modifyDecisionOptions needed for future RQC plugin

[prechelt]

The (currently half-complete) Review Quality Collector generic plugin needs to hook into this operation.

[CLAassistant]

All committers have signed the CLA.

[prechelt]

@asmecher wrote in the forum not to worry about this random test failure. So I'll sit back and assume I'll hear about this PR eventually.

[asmecher]

@prechelt, a couple of quick requests:

• Could you initialize the $result variable at the head of the function (e.g. to null)?
• I know this is already missing :) but please add a @return self-documentation to the function head.

Thanks!

[asmecher]

Thanks, @prechelt! Merged and ported forward to master.