Fix activity detection

The old logic was completely broken.

The pkg must not be prepended to the activity. This is invalid.
shell am start -n
com.thehomedepot/com.thehomedepot..Foundation.Controller.SetServicesActivity

The activity must not have the first bit chopped off. This is invalid:
Foundation.Controller.SetServicesActivity

The correct command is adb shell am start -n
com.thehomedepot/.Foundation.Controller.SetServicesActivity

Notice there's no prepended activity and that the string after the / starts with
a "."

Fixes #782