Add button "Report to moderator" for posts in forums

[tobifjellner]

Suggestion:
Add a button with the text Report to moderator next to posts in WP support forum.

Cons:

• More threads will be reported for moderation, so some more work for the moderators.

Pros:

• Makes it more obvious for occasional users how to report a thread. (Out of the blue adding the keyword modlook is not very obvious.)
• Much more user-friendly in localized forums, since the button will be trarnslatable.

[Clorith]

Related #1956

[SergeyBiryukov]

Duplicate of #1956.