HTML Report: Improve the way requests are related to their parent

@pmouawad ([Bug 65891](https://bz.apache.org/bugzilla//show_bug.cgi?id=65891&redirect=false)):
Currently HTML report generation works for CSV only and uses Naming policy to link a Transaction Controller with its children.

This may not be optimal at 2 levels:

- User must apply naming policy
- Doing that he loses sometimes the original information

Ideas to be enhanced:

- Add to CSV an information on hierarchy ?
- Recap in report the correspondance between Sampler Name and URL (rather specific to HTTP still)
- Other ideas ?

OS: All