config: make trusted miners selection more responsive to deal history

[peterVG]

Assuming I have the following settings in my default config:

      "repFactor": 3
      "trusted_miners":[
            "f015927",
            "f029404",
            "f01238",
            "f01247",
            "f01272",
            "f01278",
            "f01782",
            "f01800",
            "f02301",
            "f02388",
            "f02401",
            "f02416",
            "f02492"]

Powergate will always attempt to make new deals with the first three miners in the list ("f015927", "f029404", "f01238"), even if it had problems closing deals with those miners or if the deal process is very lengthy. It may never try miners at the bottom of this list.

It would be nice if Powergate skipped miners in the Trusted list altogether if they had failed deals (until the admin has a chance to manually move those to the Excluded list).

It would also be useful if Powergate could remember which miners on the list had successful, quick deals and try those first with every new push.

A simple quick fix could also be for Powergate to remember at what index point of the trusted miners array it had left off and start a new push from the next index point, so that it at least cycles through the whole trusted miners list rather than just using the first x on the list, where x = RepFactor.