refs #314, fromQVariant / location of toQVariant

* renamed fromQVariant to convertFromQVariant, the "from" methods imply the object is changed (fromJson, fromString ..)
* implemented fromQVariant - changing the object by QVariant
* moved toQVariant into PQ template
* free function setFromQVariant

src/blackmisc/blackmiscfreefunctions.h

@@ -107,6 +107,18 @@ namespace BlackMisc
      */
     QString qVariantToString(const QVariant &qv, bool i18n = false);
 
+    /*!
+     * Checked version from QVariant
+     */
+    template <class T> void setFromQVariant(T *value, const QVariant &variant)
+    {
+        Q_ASSERT(variant.canConvert<T>());
+        if (variant.canConvert<T>())
+        {
+            (*value) = variant.value<T>();
+        }
+    }
+
     /*!
      * Fix variant. Required if a variant "comes in" via DBus,
      * and represents a QDBusArgument rather than the real type.