Support for the region editing mode

[MinyazevR]

Implement new mode to edit regions, that can be enabled by the dedicated button (a corresponding option in settings must be turned on, ATM). A brief demonstration:
demo.webm

1. In this mode, one can resize and move regions on the scene. This mode does not work (intentionally) when the world configuration is read only ("an exercise"). If a custom region was initially visible, it will remain visible regardless of the mode, but it will not be editable outside the region editing mode.
2. In this mode, ellipses and rectangles have a context menu:
   2.1 Convert to region. An ellipse or rectangle drawn by the user is converted into an region of the corresponding shape, and the figure itself disappears from the scene:
   covert_to_region.webm
   2.2 Bind to region. In this case, a dependent (accompanying) region of the same shape is created for the selected shape, and the ellipse or rectangle itself does not disappear from the scene. This functionality is useful in typical cases where a rectangle or ellipse is placed exactly over a region that is later used in constrains to check if some object is inside or outside of the corresponding original shape.
   bind_to_region.webm

3.1 The first type of region is serialized into a familiar format, becoming an independent region:

<region id="war_zone" type="rectangle" height="4000" width="4000" x="-150" y="-2000" visible="false" color="#0000ff" filled="true"/>
			<region id="start_zone" type="ellipse" height="300" width="300" x="-150" y="-150" visible="true" color="#00ff00" filled="true"/>

3.2. The second type of regions is serialized into a simpler construct, that is designed to be user-friendly. It is only necessary to specify boundItem="id" attribute, where id is the name of an existing ellipse or rectangle in the same WorldModel.xml:

<colorFields>
    <rectangle fill-style="solid" stroke="#ffff0000" id="rectangle1" begin="313:-148" end="2:156" stroke-width="6" fill="#ffff0000" 
         stroke-style="solid"/>
    </colorFields>
    <regions>
        <region id="region1" filled="true" text="my bound region" textX="0" textY="0" visible="false" type="bound" 
            boundItem="rectangle1"/>
     </regions>