Add toggle for TinyPNG compression

[myraiganai]

Hi there. I just have a small suggestion for this plugin. When exporting an artboard, image or whatever, it would be nice to have a nice checkbox in the export dialogue that you can turn on or off, which decides if the image will be compressed or not.

Sometimes we have to further edit images we export from Sketch in Photoshop or some other program and a lossless file would be better for that. Uninstalling the plugin every time you want to do so is a hassle, though.

I hope you consider this and I also want to say thanks for this great plugin.