polygon tool: double-click too sensitive

[bertsky]

One of the most used tools is probably the polygon drawer. However, there are some practical nuisances here IMO:

• there is no way to "undo" the last vertex
• there is no way to cancel the final closure
• the time and distance for the double click rule are way too sensitive

(In effect, I often have to redo long polgons simply because LAREX thought the next vertex was the final one.)

[maxnth]

I agree, the default time / distance delta values for double clicks were a bit funky, I lowered them significantly and users are now able to set these values themselves starting with a0e6e69.