Display-->Goto Position dialog should accept + as well as - for number prefixes #1656

While it is allowed to enter co-ordinates in Display-->Goto Position as, for example, "-22000,10000" it is an error to type "-22000,+10000". For entering co-ordinates from external sources (of pre-computed positions, for example) it would be nice to allow the flexibility of an optional leading '+' symbol.

KLayout 0.28.17 on macOS