In most cases getBaseObject() is used with an exception handler which
only detects if it failed but not the reason. This modification allows
to use it without excess exception handlers.
Also add the same parameter to SketchBased::getVerifiedSketch().
The function getBaseShape() is removed and replaced with getBaseObject()
because it doesn't make a lot of scense: getBaseShape() masked the
base's class implementation (rather than redefine a virtual) which was
better in words of code reuse.
Also BaseFeature and Base properties relations are defined now in a
little another way.
