Auto add file extension when save - issue #1399 (#1521)

* draft of saving with auto added extension

* taking care of file extension, prepared option to use, WIP

* added save last used extension, cleaning needed

* cleaned

* some cleaning

* clang-formatted

* fixed unnecesary  ] in extension

* info about cancel instead of error msg

* changed regex to qstr operations, declaring filters as variables

* added cons to variables

* applied clang-formatt

src/utils/confighandler.cpp

@@ -544,6 +544,18 @@ void ConfigHandler::setUseJpgForClipboard(const bool value)
     m_settings.setValue(QStringLiteral("useJpgForClipboard"), value);
 }
 
+void ConfigHandler::setSaveAsFileExtension(const QString& extension)
+{
+    m_settings.setValue(QStringLiteral("setSaveAsFileExtension"), extension);
+}
+
+QString ConfigHandler::getSaveAsFileExtension()
+{
+    return m_settings
+      .value(QStringLiteral("setSaveAsFileExtension"), QString(".png"))
+      .toString();
+}
+
 void ConfigHandler::setDefaultSettings()
 {
     foreach (const QString& key, m_settings.allKeys()) {