Add halfop checking

Changed as per Tyrope's suggestion to add halfop for allowed commands.

Not sure if halfops can also quiet someone but from searching searching on google I found:
Halfops have the ability to change the channel topic, and to kick/ban anyone from the channel who isn't an operator.

willie/modules/adminchannel.py

@@ -11,7 +11,7 @@
 from __future__ import unicode_literals
 
 import re
-from willie.module import commands, priority, OP
+from willie.module import commands, priority, OP, HALFOP
 from willie.tools import Nick
 
 
@@ -63,7 +63,7 @@ def voice(bot, trigger):
     """
     if bot.privileges[trigger.sender][trigger.nick] < OP:
         return
-    if bot.privileges[trigger.sender][bot.nick] < OP:
+    if bot.privileges[trigger.sender][bot.nick] < HALFOP:
         return bot.reply("I'm not a channel operator!")
     nick = trigger.group(2)
     channel = trigger.sender
@@ -80,7 +80,7 @@ def devoice(bot, trigger):
     """
     if bot.privileges[trigger.sender][trigger.nick] < OP:
         return
-    if bot.privileges[trigger.sender][bot.nick] < OP:
+    if bot.privileges[trigger.sender][bot.nick] < HALFOP:
         return bot.reply("I'm not a channel operator!")
     nick = trigger.group(2)
     channel = trigger.sender
@@ -97,7 +97,7 @@ def kick(bot, trigger):
     """
     if bot.privileges[trigger.sender][trigger.nick] < OP:
         return
-    if bot.privileges[trigger.sender][bot.nick] < OP:
+    if bot.privileges[trigger.sender][bot.nick] < HALFOP:
         return bot.reply("I'm not a channel operator!")
     text = trigger.group().split()
     argc = len(text)
@@ -149,7 +149,7 @@ def ban(bot, trigger):
     """
     if bot.privileges[trigger.sender][trigger.nick] < OP:
         return
-    if bot.privileges[trigger.sender][bot.nick] < OP:
+    if bot.privileges[trigger.sender][bot.nick] < HALFOP:
         return bot.reply("I'm not a channel operator!")
     text = trigger.group().split()
     argc = len(text)
@@ -177,7 +177,7 @@ def unban(bot, trigger):
     """
     if bot.privileges[trigger.sender][trigger.nick] < OP:
         return
-    if bot.privileges[trigger.sender][bot.nick] < OP:
+    if bot.privileges[trigger.sender][bot.nick] < HALFOP:
         return bot.reply("I'm not a channel operator!")
     text = trigger.group().split()
     argc = len(text)
@@ -263,7 +263,7 @@ def kickban(bot, trigger):
    """
     if bot.privileges[trigger.sender][trigger.nick] < OP:
         return
-    if bot.privileges[trigger.sender][bot.nick] < OP:
+    if bot.privileges[trigger.sender][bot.nick] < HALFOP:
         return bot.reply("I'm not a channel operator!")
     text = trigger.group().split()
     argc = len(text)
@@ -297,7 +297,7 @@ def topic(bot, trigger):
     purple, green, bold = '\x0306', '\x0310', '\x02'
     if bot.privileges[trigger.sender][trigger.nick] < OP:
         return
-    if bot.privileges[trigger.sender][bot.nick] < OP:
+    if bot.privileges[trigger.sender][bot.nick] < HALFOP:
         return bot.reply("I'm not a channel operator!")
     text = trigger.group(2)
     if text == '':