Implemented .linkonly (as an alternative to .imageonly). Updated pokaman with latest generations. Updated responses, fixed some warnings

src/NadekoBot/data/strings/commands/commands.en-US.yml

@@ -2166,7 +2166,7 @@ imageonlychannel:
     Users who send more than a few non-image messages will be banned from using the channel. 
   args:
     - ""
-linksonlychannel:
+linkonlychannel:
   desc: |-
     Toggles whether the channel only allows links.
     Users who send more than a few non-link messages will be banned from using the channel. 

src/NadekoBot/data/strings/responses/responses.en-US.json

@@ -971,7 +971,9 @@
   "favorites": "Favorites",
   "tags": "Tags",
   "imageonly_enable": "This channel is now image-only.",
+  "linkonly_enable": "This channel is now link-only.",
   "imageonly_disable": "This channel is no longer image-only.",
+  "linkonly_disable": "This channel is no longer link-only.",
   "deleted_x_servers": "Deleted {0} servers.",
   "curtr_gift": "Gift from {0} [{1}]",
   "curtr_award": "Awarded by bot owner {0} [{1}]",