use platform independent UTF-8 coding

GUI/Models/Unit.cpp

@@ -63,15 +63,15 @@ QString unitAsString(const Unit& unit)
     case Unit::nanometer:
         return "nm";
     case Unit::nanometerPower2:
-        return "nm²";
+        return u8"nm\u00B2";
     case Unit::nanometerPowerMinus2:
-        return "1/nm²";
+        return u8"1/nm\u00B2";
     case Unit::angstrom:
-        return "\303\205";
+        return u8"\u00c5";
     case Unit::angstromPower2:
-        return "\303\205²";
+        return u8"\u00c5\u00B2";
     case Unit::angstromPowerMinus2:
-        return "1/\303\205²";
+        return u8"1/\u00c5\u00B2";
     case Unit::degree:
         return "°";
     case Unit::radiant:

GUI/Views/SampleDesigner/LayerOrientedSampleEditor.cpp

@@ -58,7 +58,7 @@ LayerOrientedSampleEditor::LayerOrientedSampleEditor(QWidget* parent)
 
     m_asAngstromAction = new QAction(this);
     m_asAngstromAction->setIcon(QIcon(":/images/unit_angstrom.svg"));
-    m_asAngstromAction->setToolTip("Use \303\205ngstrom as unit (where applicable)");
+    m_asAngstromAction->setToolTip(u8"Use \u00c5ngstrom as unit (where applicable)");
     connect(m_asAngstromAction, &QAction::toggled, this,
             &LayerOrientedSampleEditor::onUnitActionToggled);
     m_asAngstromAction->setCheckable(true);

GUI/mainwindow/actionmanager.cpp

@@ -264,7 +264,7 @@ void ActionManager::onAboutToShowSettingsMenu()
     };
 
     addUnitAction("Use nanometer as default unit", false);
-    addUnitAction("Use \303\205ngstrom as default unit", true);
+    addUnitAction(u8"Use \u00c5ngstrom as default unit", true);
 
     m_settingsMenu->addSeparator();