Add a means of filtering failures on a per-component basis (fixes #34…

[kloots]

Add a means of filtering failures on a per-component basis (fixes #34). Provide a means of logging DOM element references (fixes #35).

[angus-c]

Can take advantage of ES6 to clean the options code up in several places

e.g.

Instead of:

var filterFailures = (failureInfo, options) => {
  var failures = failureInfo.failures;
  var filterFn = options.filterFn &&
        options.filterFn.bind(undefined, failureInfo.name, failureInfo.id);

  if (filterFn) {
    failures = failures.filter(filterFn);
  }

  return failures;
};

var filterFailures = ({failures, name, id}, {filterFn}) => {
  var filterFn = filterFn && filterFn.bind(undefined, name, id);

  if (filterFn) {
    failures = failures.filter(filterFn);
  }

  return failures;
};

[angus-c]

merging - this can be addressed separately