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

This commit creates new separate "Ellips"  type, which allows to:
- hide a dedicated ellipsis rectangle drawing logic in a method
  associated only with "Ellips" objects
- distinguish ellipses and rectangles by their types, not by the
  place they come from

The name ("Ellips") has no "e" at the end because "Ellipse"
conflicts with a painting with the same name, 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.

This is a helper function required for some future changes.

DrawingPrimitive is a common interface for the parts from which
component's appearence is built: qucs::Line, qucs::Arc, qucs::Rect,
qucs::Ellips, qucs::Text. With this commit they a turned from
"dumb" POD to more "smart" objects. Common interface also allows
to hide drawing logic and make drawing more convenient and easy
for client code.

Schematic::drawContents is the root of the "drawing" call stack:
starting from this function the QPainter is passed down to diagrams,
components, paintings, etc., using the QPainter-base "paint" methods
prepared in previous commits. So, in this commit we're basically
connect everyhing together to make the new drawing subsystem.

After switching everything to drawing using bare QPainter, a lot
of ViewPainter-based stuff became unused and basically obsolete,
including the ViewPainter itself.

These functions became unused after switching to QPainter-based
drawing and printing.