Refactor how the debug is handled

[Taluu]

Fixes #24 : Move the DebugRest context into a proper listener

• Move the damn thing
• Change the necessary tag from @api to @http
• Make it work for all kind of scenarios (Background, Scenario and ScenarioOutline)
• Debug why on ScenarioOutline only the last request is debugged (and not the other ones)
• Add more specific debug options (like something allowing to debug moar, through composition : see Refactor how the debug is handled #25 (comment))
• Rename the --api-debug into --behapi-debug (as --debug is already taken, and was changed thanks to @lunika in rename debug option in full-debug #1)

[Taluu]

todo : add some sort of separator ? otherwise it goes

| Request: ...
| Request Content-Type: ....
| Response status: ...
| Response Content-Type: ...

{
...
}
| Request: ...
| Request Content-Type: ....
| Response status: ...
| Response Content-Type: ...

{
...
}

Or maybe another (!) line break... ?

[Taluu]

Another thing that is quite bothersome : With passing the Debug into a listener, we lose the possibility to erase it with custom headers.

so todo : have something like a composition (sub services ?) to add debug possibilities, which would (re)define the getDebug method

[Taluu]

To do in a later pass : using Behat's printers instead of doing echos (better handling of errors, outputs, and all)