It is now possible to report comments

[x] It's not possible to report comment
[x] The e-mail received by the podmin should contain a link to /post_report
[x] The report is sent even if the user cancel (see #4720)
[x] Renamed PostReport to Report
[x] Added report button to SPV
[ ] Need some tests for SPV
[x] Updated rspec for the controller

refs diaspora/diaspora#4732
refs diaspora/diaspora#4710
refs diaspora/diaspora#4711
refs diaspora/diaspora#4517