Merge pull request #505 from denizzzka/const_adding

Const adding, bulk 2

src/dlangui/platforms/android/androidapp.d

@@ -48,7 +48,7 @@ class AndroidWindow : Window {
 
     protected dstring _caption;
     /// returns window caption
-    override @property dstring windowCaption() {
+    override @property dstring windowCaption() const {
         return _caption;
     }
     /// sets window caption

src/dlangui/platforms/ansi_console/consoleapp.d

@@ -37,7 +37,7 @@ class ConsoleWindow : Window {
     }
     private dstring _windowCaption;
     /// returns window caption
-    override @property dstring windowCaption() {
+    override @property dstring windowCaption() const {
         return _windowCaption;
     }
     /// sets window caption

src/dlangui/platforms/common/platform.d

@@ -263,7 +263,7 @@ class Window : CustomEventTarget {
     @property int width() const { return _dx; }
     @property int height() const { return _dy; }
     @property uint keyboardModifiers() const { return _keyboardModifiers; }
-    @property Widget mainWidget() { return _mainWidget; }
+    @property inout(Widget) mainWidget() inout { return _mainWidget; }
     @property void mainWidget(Widget widget) {
         if (_mainWidget !is null) {
             _mainWidget.window = null;
@@ -366,7 +366,7 @@ class Window : CustomEventTarget {
     /// show window
     abstract void show();
     /// returns window caption
-    abstract @property dstring windowCaption();
+    abstract @property dstring windowCaption() const;
     /// sets window caption
     abstract @property void windowCaption(dstring caption);
     /// sets window icon

src/dlangui/platforms/dsfml/dsfmlapp.d

@@ -49,7 +49,7 @@ class DSFMLWindow : dlangui.platforms.common.platform.Window {
     }
 
     /// returns window caption
-    override @property dstring windowCaption() {
+    override @property dstring windowCaption() const {
         // TODO
         return ""d;
     }

src/dlangui/platforms/sdl/sdlapp.d

@@ -490,7 +490,7 @@ class SDLWindow : Window {
 
     protected dstring _caption;
 
-    override @property dstring windowCaption() {
+    override @property dstring windowCaption() const {
         return _caption;
     }
 

src/dlangui/platforms/windows/winapp.d

@@ -517,7 +517,7 @@ class Win32Window : Window {
         return _hwnd == GetForegroundWindow();
     }
     
-    override @property dstring windowCaption() {
+    override @property dstring windowCaption() const {
         return _caption;
     }
 

src/dlangui/platforms/x11/x11app.d

@@ -625,7 +625,7 @@ class X11Window : DWindow {
         return _isActive;
     }
 
-    override @property dstring windowCaption() {
+    override @property dstring windowCaption() const {
         return _caption;
     }