GUI: Beam intensity value validation fixed

This resolves #184 (closed) .

Also fixes a bug, similar to #267 (closed) for changing intensity from keyboard.

GUI/View/Common/FixupDoubleValidator.cpp

+#include "FixupDoubleValidator.h"
+
+FixupDoubleValidator::FixupDoubleValidator(QObject *parent)
+    : QDoubleValidator(parent)
+{
+
+}
+
+FixupDoubleValidator::FixupDoubleValidator(double bottom, double top, int decimals, QObject *parent)
+    : QDoubleValidator(bottom, top, decimals, parent)
+{
+
+}
+
+void FixupDoubleValidator::fixup(QString &input) const
+{
+    emit fixupSignal();
+}