We need some easier method for all-day usage, in addition to existing
point-and-click method. Also added mouse button filter for connection
lines.

Fixed connection line, but forgot about separate type for tranzient draggable type.

Use only necessary space if icons are displayed.
Reserve space for text spacing.

Here and there it had some magical values, like 12.
Now m_port_width means distance between side port edges. For polygon
type it means distance between outer edge and corner point.

Distance between ports is now set correct, and may be configured in
theme (value 0 will place them side to side or corner to corner, without
intersetions).

Box port placing part in updatePositions() is also compacted.

Caused lone input port to be not covered by client box

Bottom space includes port spacing too. Final bottom space is biggest of
port spacing, rounding, 2. Honor header shift due to line weight.
Compacted spacingT collect code.

Unclosed paths have some issues, when taking part in intersections,
so stroker seems to be only solution for now.

Draw highlight outline, for if outline is empty (Qt.NoPen), highlight entire background.
TODO: Do we need full bg/fg/outline hover-highlighting support?

Previous square cap style caused it to be drawen slightly out of end
point, and that part sometimes appeared above port, sometimes not
(usually if you select one port, connection covers port on another
side).

Use ready values for right and left sides, also making code slightly
better readable (probably subjective though).

Group box may get non-integer coordinates if, e.g. moved with scaled viewport.
When it happens, previously sharp lines between to draw between pixels,
while previously blurred lines may reversly get a sharp look.

When in scaled state, graphics still may be badly-antialiased though.

Text in port is aligned by center.
In group it is centered in header rect.
When icon is supported, text is aligned vertically with it,
and centered between icon and right group edge.

There problem with intersection, causing absent outline from one side, if not using that magical value 0.001 (any non-zero)

Clipping is enabled automatically, when clip shape is set.

Polygon was not enclosed automatically, when added to path.

What about to deliver to theming, wether ports cover group edge or not?

When drawen outside, free space between ports is busy.
But when inside, outline is overlaped with text, so themes need bigger height to fix that.

Necessary for classic theme. Now it will look like in latest patchage/ingen series.

Smaller value is guessed by distance between bottom box side and ports.

The drawRect() doesn't have variant, using qreal values, but it accepts QRectF. Even for integer coordinates it uses subpixel positioning, thus always placing them exactly between pixels.