Del key and add commands

[moreApi]

Controls: delete key to delete nodes

closes #473

AddCone,AddCylinder,MenuWeights: Add Cylinder and Cone menu entries

closes #487

[moreApi]

The cylinder looks a bit shitty because its missing lids. scenerygraphics/scenery#556

[kephale]

I leave the choice to @moreApi, but I favor adding a warning before object deletion (at least for using the delete key).

[kephale]

Do we want to warn the user? I think Blender throws up a dialog before deletion. This could be a call to the DeleteObject command and we could have that command contain the dialog warning?

[kephale]

FWIW, I would also be fine with merging this and creating an issue to track the need for deletion warning dialogs.

[moreApi]

I would prefer an undo option instead but that probatly requires it own hackerton^^
A warning could be quite annoing if one wants to delete many things. But the delete key also only works if the focus is on the scenery frame that is annoying anyway.

[moreApi]

Accidentally deleting the node you fiddled with the last hour would be the most annoing though... Therefore I vote for havig a warning.

[moreApi]

Do you know by heart how to display such a warning? I am not familiar with that.

[moreApi]

Also I did not use the delete command in the key binding. Maybe that needs also to be fixed.

[kephale]

Maybe try JOptionPane.showOptionDialog

[kephale]

IMHO it is fine to not use the DeleteObject command as well, but then the dialog could be part of deleteNode toggled by a keyword argument.

[moreApi]

ok so now the user has to confirm a delete if it is triggerd by a key press. And the button descriptions would make my human interaction professor proud.

@kephale if you are also happy you are free to merge.