Add the following members (with get/set methods):
    Bool_t fSelectViaFrame; //  Allow selection via frame.
    Bool_t fHighlightFrame; //  Highlight frame when object is selected.
  Document frame-box, the new members and secondary-selectability.

* TEveBoxSet:
  Add the following member (with get/set methods):
    Int_t  fBoxSkip; // Number of boxes to skip for each drawn box during scene rotation.

* TEveDigit/Quad/BoxSetGL:
  Move common code for deciding whether the frame should be drawn into
    TEveDigitSetGL::DrawFrameIfNeeded().
  Implement box-skipping for box-set.


git-svn-id: http://root.cern.ch/svn/root/trunk@40305 27541ba8-7e3a-0410-8455-c3a389f83636