Visualization - redesign of 2d layers in TKV3d

test bugs vis bug25136 //color scale in overlay
vrect r //2d rectangle in underlay

Current implementation of 2d layers consists of Visual3d_Layer, V3d_LayerMgr, Visual3d_layerItem. There are 2 types of layers: Overlayer and Underlayer. It is possible to draw following elements in these layers: verticies, polylines, rectangles and text (new implementation should be able to draw them too).
 There are next cons in current implementation:
  -Layer items redraw on each call (no buffering)
  -No interaction and selection
  -Cant control OpenGl resources
 It would be nice to have next features:
  *Ability to hide and display the whole layer
  *Ability to select and interact with layer items
  *Ability to have multi-level layers
 One of possible ways to solve cons is to implement 2d layers as AIS objects:
  +Selection and interaction
  +Buffering
  +Display priority
  +Driven by AIS Context
 I suggest to make this in the following way:
  1) New class AIS_2dLayer which inherits from AIS_InteractiveObject.
  2) AIS_2dLayer will be able to draw some standard objects (e.g. color scale).
  3) New class AIS_2dLayerObject which inherits from AIS_InteractiveObject.
  4) AIS_2dLayer keeps a list of AIS_2dLayerObject.
  5) AIS_2dLayerObject has high-level drawing methods (e.g. DrawRectangle, DrawTriangle).
  6) AIS_2dLayerObject uses Graphic3d_PrimitiveArray for buffering and drawing.
  7) New methods for AIS_InteractiveContext which work with given AIS_2dLayer and iterate on his list of AIS_2dLayerObject (e.g. DisplayLayer(AIS_2dLayer)).