Merge of EVE-dev branch.

Merge of EVE-dev branch.

From this point onward root-5.20 is required for compilation.

Major changes that might be relevant for developers having EVE related
code outside of AliRoot/EVE.

1. Remove calls to TEveElement::UpdateItems(). This method was
obsolete and has been removed.

2. Replace calls to TEveElement::GetNChildren() with
NumChildren(). The method has been renamed to use the same naming
conventions as other methods of the same type.

3. Remove all explisit casts to Color_t that were needed because of
overloading of color-setting functions (Color_t, Pixel_t). As this was
annoying, the methods taking Pixel_t were renamed to
SetXyzzPixel(Pixel_t).

4. Minor changes in internals of TGLViewer and its window-system
interface.