States terminology improvements

[StefanoFalsetto-CKHIOD]

The terms used into the returned states of conditional call forwarding are not standard. Maybe in next version we can change them using HLR terminology?
My proposal:

• from conditional_unavailable to conditional_not_reachable
• from conditional_no_reply to conditional_no_answer

[FabrizioMoggio]

Agreed.

[FabrizioMoggio]

New Issue to fix what discussed here: #111

[bigludo7]

Fine for me as well

[FabrizioMoggio]

Implemented