Add ability to save to external storage

[manekineko2]

For devices that have external storage, it would be helpful to have the option to choose to save to external storage instead.

[RyanDawkins]

This would be cool! How could I get working on this @xplodwild ??? (What steps would I need to take to contribute?)

[xplodwild]

UI wise, I'd say it would be good to have an "SDcard" toggle button in the Settings widget. Then, you need to change the destination in SnapshotManager.ImageSaver