BugFix and error reporting

* Fix a bug if the macro path is invalid
* reporting exeptions if somethings fail in the Draft core modules init
+ fixes #0001380: Allow to set user-defined names for constraints
Draft: fixed a bug in Draft Scale
+ fixes #0001380: Allow to set user-defined names for constraints
Draft SVG export: fix viewbox for raw output
Draft: fixed draft scale again - fixes #1385