Added script to create DMG installers

const createDMG = require('electron-installer-dmg')

const path = require('path')

const package = require('../package.json');

var opts = {

  appPath: path.join(__dirname, '../release-builds/openflexure-ev-darwin-x64/openflexure-ev.app'),

  name: package.productName,

  icon: path.join(__dirname, '../icons/mac/icon.icns'),

  out: path.join(__dirname, '../release-builds/installers', package.version)

}

createDMG(opts, function done (err) {

  if (err) {

    console.log(`Error creating dmg: ${err}`)

  }

  else {

    console.log("Done")

  }

 })

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