Use error exit code if files could not be installed

[kannes]

This enables use in scripts with proper error handling: pbt deploy -y && echo "success" || echo "fail"

Also, when used with the Plugin Reloader plugin, it won't silently swallow errors on deployment anymore but show a yellow error bar instead.

[kannes]

On hold as the error message is not printed to the log anymore in the Plugin Reloader and that ruins the intent...