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