function setState(entity, entitySelector, update) {
  if (!this.state[entity][entitySelector]) {
    this.state[entity][entitySelector] = new Store();
  }
  this.state[entity][entitySelector].setState(update);
}
@description Update the state in a given entity.
@param {string} entity - The type of entity we should save the state to.
@param {string} entitySelector - The selector of the entity.
@param {object} update - The object to merge into the state.
@example
stateManager.setState('house', 'main-house', {
  alarm: 'disarmed'
});