Implement selectors

[taco]

It would be nice if grid came with selectors out of the box.

We can consume them internally as well as export them for users.

Proposed Selectors

These were the selectors I was thinking would add most value, let me know if you can think of some others:

• getCurrentRecords
• getIsEditing
• getIsLoaded
• getPager
• getSelectedRows
• getTreeData

Implementation options

We have a couple of different ways we use the selectors. I've come up with two options, we can choose one or do both.

Option A

import { buildSelectors } from 'grid';

const gridKey = 'grid-1';

const selectors = buildSelectors(gridKey);

const mapStateToProps = state => ({
    selectedRows: selectors.getSelectedRows(state),
    isLoaded: selectors.getIsLoaded(state)
})

Option B

import { selectors } from 'grid';

const gridKey = 'grid-1';

const mapStateToProps = state => ({
    selectedRows: selectors.getSelectedRows(gridKey, state),
    isLoaded: selectors.getIsLoaded(gridKey, state)
})

[bencripps]

I think option A is nicer -- but I also think it would be cool if both worked?

The only one I think we should add to the selectors list is:

getEditor