1. Please test:

- polygon conversion (see below)

- check if polygon conversion undo works properly

- propedit: right click on circle, line or polygon objects (in case of 
polygon on the outline!), select propedrty editing in the context popup; 
this window is pretty much the same as in pcb-rnd

- all propedty editor edits are undoable

- in case of arc you can change angles as well, check if that works 
properly and undoable; remember: you have to start from a circle and can 
use the property editor to make it an arc. It is because I expect we will 
need full circles much more often than arcs in sch-rnd.

2. What is a polygon, drawing a polygon

A polygon is a closed loop of lines (and later arcs, not yet supported). 
A polygon can have 2 pens, both optional: one for the outline (stroke) and 
one for fill. Since fill is optional, this means you can have a 
triangle or box specified as a polygon - this is how the rectangle 
tool already works (we do not have a rectangle object, it simply 
draws a special case polygon).

Unlike in pcb-rnd, there's no polygon clipping: no poly holes, no 
clearances, no poly bool algebra. Self intersecting polygons are still 
invalid, tho (the gui doesn't try to block you from drawing them).

At the moment we do not have a dedicated polygon draw tool, like in 
pcb-rnd. Instead we have a conversion path, similat to pcb-rnd's "convert 
to padstack" and "convert to subcircuit". Use the line tool to draw a 
closed loop of lines then select the whole thing (with drag&drop box 
selection) and use the menu: select/convert selection to/polygon. This 
will detect your loop, create a polygon matching your loop and removes the 
individual lines. The polygon inherits one of the line's stroke pen and 
no fill. Once you are finished, you typically want to right click propedit 
it to change stroke and fill.

The rationale for no-poly-tool:

- Unlike in pcb-rnd now, sch-rnd will support arcs in poly outline long 
term (not before the beta unless I run out of tasks). This will be very 
handy e.g. in drawing logic gates. (However, this is the rare case, I 
expect most polygons we ever draw would be triangles and trapezoids.) I 
do not want to have a real complicated polygon drawing tool that can 
somehow draw arcs, the same way we do not have some special footprint draw 
tool in pcb-rnd either. Whenever we need to create an object that's not 
the simplest plain thing, we just construct it by converting atoms.

- Our line tool is optimized for drawing in a continous stream of line 
segments. So drawing the initial closed loop feels very much like 
pcb-rnd's polygon tool, except we do not have a "close poly" at the 
moment. So the bulk number of clicks in the whole process is the same, and 
the conversion (with selection and the hotkey {s c p}) is just two more 
steps