Introduce a kind of workflow for Load Testing (Record / Validate / Load Test)

**UbikLoadPack support** ([Bug 62536](https://bz.apache.org/bugzilla//show_bug.cgi?id=62536&redirect=false)):
Today compared to other commercial load test tools, it may not be obvious to users how to:
- Record
- validate
- Load Test

This issue is to tackle the item and see what can be proposed.

For example:

- Maybe the recorder should be here by default and not deletable and a record button could then be added as a menu
- Also, why not always have by default a View Results Tree that is used for Debugging a script
- And finally, since a Thread Group is the mandatory component to add Test items, it should be here by default

OS: All