function findUniqueName (name, existingPropNames) {
  if (existingPropNames.indexOf(name) === -1) {
    return name
  }

  const strippedName = name.replace(/ \(copy( \d+)?\)$/, '')
  let validName = strippedName
  let i = 1

  while (existingPropNames.indexOf(validName) !== -1) {
    const copy = 'copy' + (i > 1 ? (' ' + i) : '')
    validName = strippedName + ' (' + copy + ')'
    i++
  }

  return validName
}
Find a unique name. Suffix the name with ' (copy)', '(copy 2)', etc
until a unique name is found
@param {string} name
@param {Array} existingPropNames    Array with existing prop names