nextId (prefix) {
    // TODO: we could create more beautiful ids?
    // however we would need to be careful as there might be another
    // element in the HTML coming with that id
    // For now we use shas
    return this.state.uuid(prefix)
  }
Generates an id. The generated id is unique with respect to all ids generated so far.

@param {String} prefix
@return {String} the generated id