Use only first page of RTD docs for BPMN, leave the remaining sites untouched. - [x] Rename first page - [x] Include overview BPMN for data processing - [x] Include overview BPMN for pre-processing - [x] include BPMNs for each section DP - [x] include BPMNs for each section in Pre-processing - [ ] display release with finished documentation, probably v0.4.6