Add board locking, update tests, and update clean() methods

* Boards can be locked from allowing posts - this is can be useful for
  things like archived boards or locking down in the event of an
  emergency
* Some validation checks for new posts are from the reply/thread form to
  the Post model's clean() method
* Add some new tests, I've really been falling behind on those

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

board/models.py

@@ -58,6 +58,8 @@ class Board(models.Model):
     # Auto-sink threshhold. This is the number of replies that a thread can have
     # before it stops being bumped.
     autosink = models.IntegerField(default=300)
+    # Whether this board is read-only or not.
+    readonly = models.BooleanField(default=False)
 
     @property
     def threads(self):
@@ -115,10 +117,10 @@ class Post(models.Model):
     # Thumbnail
     thumbnail = models.ImageField(upload_to=thumbs_upload, editable=False, null=True)
     # Original image name
-    original_image_name = models.CharField(max_length=255, null=True)
+    original_image_name = models.CharField(max_length=255, null=True, blank=True)
     # Image width and height
-    image_width = models.IntegerField(null=True)
-    image_height = models.IntegerField(null=True)
+    image_width = models.IntegerField(null=True, blank=True)
+    image_height = models.IntegerField(null=True, blank=True)
 
     class Meta:
         permissions = [
@@ -183,6 +185,15 @@ class Post(models.Model):
                 _("Image supplied is too large. Maximum image size is %(max)s"),
                 params={"max": settings.MAX_UPLOAD_SIZE},
             )
+        # Check if board is readonly
+        if self.board.readonly:
+            raise ValidationError(
+                _("This board is in readonly mode, you cannot create new posts.")
+            )
+        # Check if OP is locked
+        if self.op and self.op.lock:
+            raise ValidationError(_("This thread is locked, you cannot reply to it"))
+
         # Rate limiting for posts
         # TODO BUG: if a user's last post is deleted, and it is their only post,
         # they will not hit rate limit. This could probably be abused