Make the flow-diagram correctly show that Epicardium will create
menu.py if none was found on the external flash. This means,
the menu will always be run from menu.py.
docs: Update overview diagram
The 3rd core is not used for BLE as of now so we should not document it
as such. This commit also updates the colors of Epicardium and
Pycardium to match the rest of the docs & GitLab.
