Added sharing of image resources across plugin instances

[d.healey]

Does this mean that plugins have some shared memory?

[Christoph Hart]

Yes, from now on image resources get shared. I added this to save a few bytes on iOS because Apple kills your plugin if all instances together use more than 350MB, but on Desktop it's also there.

I know where you getting at, and it will probably not work for samples :) The reason is that images is simple read-only data, while the samples might change the preload size dynamically and this might cause issues on plugins.

[d.healey]

@christoph-hart Your read my mind :)