adding image showing structure of IEPC in user manual, bugfixes in UI (disable input elements when not needed)

- engine form: use correct filebrowser instance
- vtp job: plot second fuel if available
- json writer set engine-only mode correctly
- test-project: do not use classes from GUI but already available classes from test project

new testcases for bus aux combinations A - C3b

bugfixes in gui: vbatr and vbatv exensions mixed up, loading hybrid strategy params, updating job when battery or em files are changed, update picture in battery dialog when input is changed,