add option to exclude channels with nodes

[openoms]

skip setting channels with the IDs in the feeadjuster-exclude.list file

Fixes: #165

The simplest solution I could come up with to achieve not setting all channels when running: lightning-cli feeadjust

To not create a new file a config option would need to be created for each pubkey something like:

  "options": [
    {
      "name": "exclude",
      "type": "string",
      "default": 0,
      "description": "A pubkey of a node to not adjust the channels with.",
	  "multi": true
    }

then would need to parse the multiple entries into a list.

I think it is more useful to have a separate list so the list of pubkeys don't need to be deleted if one stops using the feeadjuster temporarily.