ui: basic search view

- Added a basic SearchView (+ controller and qt implementation)
- SearchView can set the active element of other views by dispatching a message.
- SearchView adjusts its text when the active element is changed by other views.
- Added wrappers for Button and EditBox that allow the usage of simple callback functions.

src/app/qt/element/QtButton.cpp

@@ -0,0 +1,23 @@
+#include "qt/element/QtButton.h"
+
+QtButton::QtButton(QWidget *parent)
+	: QPushButton(parent)
+	, m_onClick(nullptr)
+{
+	connect(this, SIGNAL(clicked()), this, SLOT(slotOnClick()));
+}
+
+QtButton::~QtButton()
+{
+}
+
+void QtButton::setCallbackOnClick(std::function<void(void)> callback)
+{
+	m_onClick = callback;
+}
+
+void QtButton::slotOnClick()
+{
+	if (m_onClick)
+		m_onClick();
+}