include BPMNs in RTD docs

[gplssm]

Use only first page of RTD docs for BPMN, leave the remaining sites untouched.

• Rename first page
• Include overview BPMN for data processing
• Include overview BPMN for pre-processing
• include BPMNs for each section DP
• include BPMNs for each section in Pre-processing
• display release with finished documentation, probably v0.4.6