Use isupport informations to know the user modes when joining

Also remove the duplicate send_self_join methods, user only send_user_join

src/irc/irc_user.hpp

@@ -2,6 +2,8 @@
 # define IRC_USER_INCLUDED
 
 #include <string>
+#include <map>
+#include <set>
 
 /**
  * Keeps various information about one IRC channel user
@@ -9,10 +11,12 @@
 class IrcUser
 {
 public:
+  explicit IrcUser(const std::string& name,
+                   const std::map<char, char>& prefix_to_mode);
   explicit IrcUser(const std::string& name);
-
   std::string nick;
   std::string host;
+  std::set<char> modes;
 
 private:
   IrcUser(const IrcUser&) = delete;