Add option onDropWith for plugin function iaEnabled

[nmpetkov]

It is handy in some cases plugins (AutoResize, AutoRotate, Watermark) to be enabled, but to function only if given meta key is pressed while dropping images. This is opposite to option offDropWith.

This PR adds such a possibility.

Current functionality (offDropWith) is same and new features are backward compatible.

[nao-pon]

@nmpetkov It's so nice idea! Thanks! 👍

[nmpetkov]

Thanks!
It is good to think then about something like check boxes (in toolbar?) to turn respective plugin on/off.
Then resizing, rotation and watermark can function not only when dropping images, but also when uploading by selecting with explorer.