qtquick: Added example for min-size support

Started documenting it.
There's seems to be lots of improvements to do.

For issue #262

Author: iamsergio

docs/book/src/SUMMARY.md

@@ -35,6 +35,7 @@
 - [Advanced Usage]()
   - [Custom Behaviour](custom_behaviour.md)
   - [Custom Styling](custom_styling.md)
+  - [Min/Max sizing](min_max_sizing.md)
   - [Public and Private API](private_api.md)
 ---
 - [For Developers]()

docs/book/src/min_max_sizing.md

@@ -0,0 +1,16 @@
+# min/max sizing
+
+## QtWidgets
+
+KDDW will honour min/max constraints set on the guest widget.<br>
+You can run the example `qtwidgets_dockwidgets -g` to see the max-size in action.<br>
+Setting the constraints directly on `DockWidget` is not advised.
+
+## QtQuick
+
+Minimum sizes are supported but not maximum sizes.<br>
+There's no public API to set the minimum sizes, but you can set a special property called `kddockwidgets_min_size`
+on your guest item.<br>
+For an example, run the `qtquick_dockwidgets` sample executable, then go to "File" menu, and chose `New widget with min-size`.
+
+Note that while KDDW floating windows and docked widgets will honour the min size, the main window itself won't, as that's an item completely controlled by the user. Maybe we could expose the main window's KDDW layout min/max size, then users could use that to calculate the main window's min/max.

examples/qtquick/dockwidgets/main.qml

@@ -57,6 +57,32 @@ ApplicationWindow {
                 }
             }
 
+            Action {
+                text: qsTr("Create widget with min-size")
+                onTriggered: {
+                    /// Do not use random uuids if you're planing to use layout save/restore!
+                    /// Using them here for convenience of the exercise
+                    var uniqueName = _kddwHelpers.generateUuid();
+
+                    var code = `import com.kdab.dockwidgets 2.0 as KDDW;
+                                import QtQuick 2.6;
+                                KDDW.DockWidget {
+                                    uniqueName: "${uniqueName}";
+                                    title: "min-size=" + guest.kddockwidgets_min_size
+                                    Rectangle {
+                                        id: guest
+                                        property var kddockwidgets_min_size: Qt.size(800, 200)
+                                        // property var kddockwidgets_max_size: Qt.size(800, 400) Not yet supported
+                                        color: "#85baa1";
+                                        anchors.fill: parent;
+                                    }
+                                }`;
+
+                    var newDW = Qt.createQmlObject(code, root);
+                    newDW.open();
+                }
+            }
+
             Action {
                 text: qsTr("Close All")
                 onTriggered: {
@@ -82,6 +108,7 @@ ApplicationWindow {
     }
 
     KDDW.DockingArea {
+        id: root
         anchors.fill: parent
 
         // Each main layout needs a unique id