Improve filtering for issue weight

Currently you can only select 'Any', which includes 'No'.

It should be:

• any weight => all issues (assuming not == 0)
• no weight => issues without weight set
• ..list of weights

@JobV just had a quick look at this one but it looks to me is EE only?

@jameslopez correct, this issue should be moved :)

cool! Closing this as opened up a new issue on EE: https://gitlab.com/gitlab-org/gitlab-ee/issues/274

Status changed to closed