Add user post wiping

If a user has spammed a lot of posts and made a mess of the board, this
will allow us to delete all posts by the offending user from the same
IP.

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

board/models.py

@@ -134,6 +134,7 @@ class Post(models.Model):
             ("set_sticky", "Can sticky post"),
             ("set_bump", "Can bumplock post"),
             ("set_lock", "Can lock post"),
+            ("wipe_user", "Can wipe all posts by a user"),
         ]
 
     def save(self, *args, **kwargs):