Fix generator test generation, configlet command

[Bajger]

4 problems encountered during exercise re-generation:

• test class generated with tag - it creates problem when moving to solution directory and it should be in same package/tag as solution class
• configlet command needs to change its invocation (from parent directory) and needs to start with './'
• optional: hint comment is overwritten by TBD (need to keep existing hint when regenerating)
• generator removes exercises/practice/darts/.class.st which determines template for empty solution file (need to revert changes on this file)