turning a lot of includes into forward declares

src/providers/irc/AbstractIrcServer.hpp

@@ -1,6 +1,5 @@
 #pragma once
 
-#include "common/Channel.hpp"
 #include "providers/irc/IrcConnection2.hpp"
 
 #include <IrcMessage>
@@ -11,6 +10,9 @@
 
 namespace chatterino {
 
+class Channel;
+using ChannelPtr = std::shared_ptr<Channel>;
+
 class AbstractIrcServer
 {
 public: