bootRepackage should declare its inputs and outputs

[toolforger]

Gradle assumes that each task declares on what inputs it depends, and what outputs it generates. If all inputs and outputs are unmodified since the last Gradle build, Gradle decides it does not need to run the task.
The savings ripples to dependent tasks, so it's worth doing.

If a task does not declare any outputs at all, Grade assumes that it does not have a useful view of inputs and outputs and always runs the task.
This seems to be what happens with the bootRepackage task:

:saturn_client:bootRepackage (Thread[Daemon Thread 4,5,main]) started.
:saturn_client:bootRepackage
Executing task ':saturn_client:bootRepackage' (up-to-date check took 0.0 secs) due to:
  Task has not declared any outputs.
Found main in run task: edvWerkstatt.EDV_WerkstattApp
:saturn_client:bootRepackage (Thread[Daemon Thread 4,5,main]) completed. Took 1.717 secs.

(The other issue defeating Gradle's up-to-date checking is #1113.)

[dsyer]

Fixed with #1113