moved slider's focusable line edit to a separate distinct reusable widget

Some of the widgets designed for Slider have uses elsewhere so now they have
been moved to allow more generic usage.

app/widget/clickablelabel/clickablelabel.cpp

@@ -0,0 +1,23 @@
+#include "clickablelabel.h"
+
+ClickableLabel::ClickableLabel(const QString &text, QWidget *parent) :
+  QLabel(text, parent)
+{
+}
+
+ClickableLabel::ClickableLabel(QWidget *parent) :
+  QLabel(parent)
+{
+}
+
+void ClickableLabel::mouseReleaseEvent(QMouseEvent *)
+{
+  if (underMouse()) {
+    emit MouseClicked();
+  }
+}
+
+void ClickableLabel::mouseDoubleClickEvent(QMouseEvent *)
+{
+  emit MouseDoubleClicked();
+}