Fixes StackOverflowError in `RegionUtils.subtract`

There are two problems in the underlying method `subtractImpl`:

- It calls the API method `subtract`, which is an unnecessary
  performance cost because `subtract` checks its input parameters
- It is not tail recursive

Fixes #1002361
Use GridLayout instead of RowLayout in ReportBugDialog

This solves the problem of weirdly displayed whitespace between widgets.
Add link to svelto in ReportBugDialog
Fix spelling mistake in constant in SdtConstants
Fixes several warnings that occur during the build

This fixes warnings due to unchecked and not exhaustive pattern
matching.
Merge pull request #884 from sschaef/fix-spelling-in-constant

Fix spelling mistake in constant in SdtConstants
Merge pull request #883 from sschaef/t-show-svelto

show svelto link in report bug dialog
Merge pull request #885 from sschaef/t-fix-build-warnings

Fixes several warnings that occur during the build
Merge pull request #882 from sschaef/t1002361-stackoverflow

Fixes StackOverflowError in `RegionUtils.subtract`