Remove unnecessary container reducer and make <Subdivide> potentially controllable

[gaearon]

This removes Container and makes layout the top-level reducer. The diff doesn't do it justice, but really all that happened is I removed Container and made what was called LayoutReducer a top-level reducer, also renaming it to be called just layout.

[gaearon]

The second commit renames constants/blenderLayoutConstants to just constants/index since there don't appear any other kinds of constants.

[gaearon]

The last commit makes reducer a named export of the package.
Now <Subdivide> acts like a chameleon:

• If you use it directly, it will create its own store and use it;
• If you connect() it to some part of the app's state, it will assume you have mounted the reducer there.

The reason I want these two modes is because Subdivide should be usable as is, but it would also be nice if I could mount its state to my existing reducer tree.

For example:

Normal usage

import React, {Component} from 'react';
import ReactDOM from 'react-dom';
import Subdivide from './index';

class IframeComponent extends Component {
  render() {
    return (
      <iframe src="index2.html" frameBorder={'0'} style={{
         width: '100%',
         height: '100%'
      }} />
    );
  }
}

ReactDOM.render(
  <Subdivide DefaultComponent={IframeComponent} />,
  document.getElementById('root')
);

Usage with connect()

import React, {Component} from 'react';
import {createStore, combineReducers} from 'redux';
import ReactDOM from 'react-dom';
import Subdivide, { reducer as subdivide } from './index';
import {connect, Provider} from 'react-redux';

const store = createStore(combineReducers({
  subdivide,
  // you app's reducers
}), {
  // haha! you can pass persisted state
  subdivide: {"rootId":"1","borderSize":1,"cellSpacing":3,"touchMargin":2,"width":612,"height":658,"panes":{"0":{"id":"0","childIds":[],"isGroup":false,"parentId":"1","splitRatio":0.7026143790849673,"top":0,"left":0,"width":429.99999999999994,"height":658,"joinDirection":false},"1":{"id":"1","childIds":["0","3"],"isGroup":true,"direction":"ROW","splitRatio":1,"top":0,"left":0,"width":612,"height":658},"2":{"id":"2","childIds":[],"isGroup":false,"parentId":"3","splitRatio":0.5136778115501519,"top":323,"left":432.99999999999994,"width":179.00000000000003,"height":334.99999999999994,"joinDirection":false},"3":{"id":"3","childIds":["4","2"],"isGroup":true,"direction":"COL","parentId":"1","splitRatio":0.29738562091503273,"top":0,"left":432.99999999999994,"width":179.00000000000003,"height":658,"joinDirection":false},"4":{"id":"4","childIds":[],"isGroup":false,"parentId":"3","splitRatio":0.48632218844984804,"top":0,"left":432.99999999999994,"width":179.00000000000003,"height":320,"joinDirection":false}},"dividers":{"0n3":{"id":"0n3","top":0,"left":429.99999999999994,"width":3,"height":658,"beforePaneId":"0","afterPaneId":"3","beforeRatio":0.7026143790849673,"afterRatio":0.29738562091503273,"direction":"ROW","parentSize":612},"4n2":{"id":"4n2","top":320,"left":432.99999999999994,"width":179.00000000000003,"height":3,"beforePaneId":"4","afterPaneId":"2","beforeRatio":0.48632218844984804,"afterRatio":0.5136778115501519,"direction":"COL","parentSize":658}}}
});

class IframeComponent extends Component {
  render() {
    return (
      <iframe src="index2.html" frameBorder={'0'} style={{
         width: '100%',
         height: '100%'
      }} />
    );
  }
}

const ConnectedSubdivide = connect(
  // Tell where to grab the relevant state
  state => ({ layout: state.subdivide })
)(Subdivide);

ReactDOM.render(
  <Provider store={store}>
    <ConnectedSubdivide DefaultComponent={IframeComponent} />
  </Provider>,
  document.getElementById('root')
);