Add emojis to autocomplete

Improve autocomplete:
 - Add space after autocompleted item
 - Emotes starting with `:` can now be autocompleted properly (i.e. emojis)

src/completionmanager.hpp

@@ -28,6 +28,8 @@ public:
         return this->emotes.size();
     }
 
+    void addString(const std::string &str);
+
     QVector<QString> emotes;
 };