Utilize templates for Settings class

Use boost2::signals for the valueChanged signal (a LOT less messy to
        deal with than qt signals)
Remove unused settings classes (BoolSetting, FloatSetting, IntSetting,
        StringSetting)

What's left: Implement the remaining signals

settings/setting.h

@@ -3,22 +3,61 @@
 
 #include <QSettings>
 #include <QString>
+#include <boost/signals2.hpp>
 
 namespace chatterino {
 namespace settings {
 
-class Setting : public QObject
+class BaseSetting
 {
-    Q_OBJECT
-
 public:
-    explicit Setting(const QString &name)
-        : name(name)
+    virtual void save(QSettings &settings) = 0;
+    virtual void load(const QSettings &settings) = 0;
+};
+
+template <typename T>
+class Setting : public BaseSetting
+{
+public:
+    Setting(const QString &_name, const T &defaultValue)
+        : name(_name)
+        , value(defaultValue)
     {
     }
 
-    virtual void save(const QSettings &settings) = 0;
-    virtual void load(const QSettings &settings) = 0;
+    const T &
+    get() const
+    {
+        return this->value;
+    }
+
+    void
+    set(const T &newValue)
+    {
+        if (this->value != newValue) {
+            this->value = newValue;
+
+            this->valueChanged(newValue);
+        }
+    }
+
+    virtual void
+    save(QSettings &settings) final
+    {
+        settings.setValue(this->getName(), QVariant::fromValue(this->value));
+    }
+
+    virtual void
+    load(const QSettings &settings) final
+    {
+        QVariant newValue = settings.value(this->getName(), QVariant());
+        if (newValue.isValid()) {
+            assert(newValue.canConvert<T>());
+            this->value = newValue.value<T>();
+        }
+    }
+
+    boost::signals2::signal<void(const T &newValue)> valueChanged;
 
 protected:
     const QString &
@@ -29,8 +68,10 @@ protected:
 
 private:
     QString name;
+    T value;
 };
-}
-}
+
+}  // namespace settings
+}  // namespace chatterino
 
 #endif  // SETTING_H