Make debug.testing default (& rm the option) add new production.strict option

[kilrau]

As discussed on discord, I'd like to turn things around: instead of being very strict and gradually adding more things to debug.testing because they hinder real-world usage, I'd open it up to the best degree possible and slowly start getting stricter once things mature.

I propose to remove the current debug.testing option and make the behavior behind this flag the the default behavior.

Some of the features this is disabling will become useful though in future, that's why I propose to add a new production.strict option that enables the following:

• peers mutually banning each other because of severe L2 payment errors like "NO ROUTE FOUND".
• disabling currencies for a certain peer because of swap failure
• removing all orders of a peer because of swap failure