Added clear command

[mrmike]

Added clear comment for clearing app data like cache, databases and shared preferences. To use clear command rooted device or emulator is required.

[mttkay]

Love the idea. One thing I might change: it looks like you're relying on default_package to be set, but it might be nil. We should probably catch that case and expect a package argument instead?

[mrmike]

Sure, I will change that.

[mrmike]

Hi Matthias,

I've added argument handling for clear command.

[mttkay]

Thanks!