Remove preferred size and default button size

Replace alignment data in horizontal and vertical layout with double value
Add convenient size(GuiElement, ReadableDimension) method to custom layout

src/main/java/de/johni0702/minecraft/gui/container/AbstractGuiContainer.java

@@ -196,7 +196,7 @@ public abstract class AbstractGuiContainer<T extends AbstractGuiContainer<T>>
     }
 
     @Override
-    public ReadableDimension getMinSize() {
+    public ReadableDimension calcMinSize() {
         return layout.calcMinSize(this);
     }
 }