Warn if package is too large

[TwitchBronBron]

On lower-end devices, uploading very large packages can take a long time. We should consider warning users if their packages are too large. I maintain this extension, and it took me 10 minutes to realize why the app wouldn't ever sideload...

I think something like 12-15 MB is a good size. Perhaps make this size configurable, which would allow people to make it really large if they want to completely ignore the warning.

[TwitchBronBron]

This might need to happen in the roku-debug package.