SOMs and negative inputs

[CorvusPrudens]

This PR adds a SOM field to the json for targeting a specific SOM (right now either seed or patch_sm).

It also permits negative inputs when using input_min and input_max fields in an input description, e.g.:

{
  "inputs": {
    ...
    "cv5": {
      "input_min": -1,
      "input_max": 1,
      "code": "hardware.GetAdcValue(daisy::patch_sm::CV_5);"
    },
    ...
  }
}

This adjusts the scaling Oopsy does to factor in the different input range, preserving the expected behavior of the @max and @min param attributes. This addresses #60.

[stephenhensley]

closing as this is handled in #69