Make it easy to add items to an experiment

[Lawouach]

Is your feature request related to a problem? Please describe.

The Chaos Toolkit 'experiment format has become rich over the years. While the documentation has improved, it's not always easy to know how to add specific blocks.

Describe the solution you'd like

A new command line such as:

$ chaos experiment add control <name> --args X=Y 
$ chaos experiment add action <name> --to method --args X=Y 
$ chaos experiment add probe <name> --to hypothesis --args X=Y 
$ chaos experiment remove control <name>

Describe alternatives you've considered

More documentation. I think both are necessary.