Move message size limit logic to base plugin

This is beneficial for all plugins so the bot doesn't accidentally
spam things because the plugin writer didn't check their inputs

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

plugins/linkbot.py

@@ -105,7 +105,7 @@ class Linkbot(Plugin):
                 message = None
 
             if message:
-                self.send_to(conn, channel, message[:1024])
+                self.send_to(conn, channel, message)
 
 
 PLUGIN_TYPE = Linkbot