Both ellipses and rectangles are drawn from a single object named
"Area". Drawing logic looks from where it got the object: if it's
from "rectangles" container, then draw a rectangle, otherwise
draw an ellipse.

This commit creates new "Ellips" object type, separate from "Area".
It opens a way to:
- hide a dedicated ellipsis rectangle drawing logic in a method
  associated only with "Ellips" objects
- distinguish ellipses and rectangles not by their place of residence,
  but by their nature.

The name "Ellips" without "e" at the end is used because "Ellipse"
conflicts with a painting named that way, which is declared in the
same namespace. I didn't want to go into any additional trouble
and chose to go with this type of a "workaround"

Some classes have members of container types, storing "Ellips"
objects, i.e. ellipses. Just assigning a proper name.

After extracting ellipse from "Area" to a separate class, "Area"
means only a rectangle.

The goals of this are
- add a generic API for qucs::Line, qucs::Arc, qucs::Rect, qucs::Ellips
- hide drawing details from clients. If you take a look at code
  now you'll see that drawing of for example a line in Component::paint
  looks like "take this coordinate, add this nubmer to it, and call
  a method of QPainter". Drawing logic is outside, it must be written
  every time you want to draw a line.
  New API provides a way to just invoke DrawingPrimitive::draw giving
  it a QPainter and be done with drawing.