Check if params exist before setting them

[ben-kaufman]

Fix #228
I was unable to do this redundancy check for the custom schemes since I have no pre-knowledge n a "non-null" parameters which they must have. That should be fine for now but suggestions to overcome that are welcomed.

[dOrgJelli]

@ben-kaufman if you have the desired scheme parameters accessible to you in the script, for example:

const params = {
  someFlag: true,
  someNumber: 5,
  someString: "foo"
}

then you could get the has from the contract:

const hash = customScheme.getParamHash(params);

and then view the params to see if you get a missmatch:

const storageParams = customScheme.getParams(hash);
for (let param of Object.keys(params)) {
  if (storageParams[param] !== params[param]) {
    customScheme.setParams(params);
    break;
  }
}

[dOrgJelli]

I think this should work, made some assumptions about there being a common scheme interface that has getParamHash and getParams available.