Add button to ban poster, for abusing reports

[bakape]

Mods will need to be able to view reporters by mnemonic.

[Chiiruno]

For illegal reports, perhaps add a purge option, that will purge if single post, purge as thread if OP #1061. This way, we could remove showing IP in illegal report error and email.

[Chiiruno]

Assuming this is in /html/reports/:board

[Chiiruno]

Related #1125