Add webpack support

[ssalat]

Added webpack module support.

[ssalat]

Tested and works:

// Only iFrameResizer (host page)
import {iframeResizer} from 'iframe-resizer'

or

// Only iframeResizerContentWindow (iframe)
import {iframeResizerContentWindow} from 'iframe-resizer'

[skedone]

+1

[elektronik2k5]

+1 I was going to submit a similar PR to do just that - thank you @ssalat :)

[davidjbradshaw]

Released v2.8.7. Thanks.