* Block header download starting at Beacon down to Era1
details:
The header download implementation is intended to be completed to a
full sync facility.
Downloaded block headers are stored in a `CoreDb` table. Later on they
should be fetched, complemented by a block body, executed/imported,
and deleted from the table.
The Era1 repository may be partial or missing. Era1 headers are neither
downloaded nor stored on the `CoreDb` table.
Headers are downloaded top down (largest block number first) using the
hash of the block header by one peer. Other peers fetch headers
opportunistically using block numbers
Observed download times for 14m `MainNet` headers varies between 30min
and 1h (Era1 size truncated to 66m blocks.), full download 52min
(anectdotal.) The number of peers downloading concurrently is crucial
here.
* Activate `flare` by command line option
* Fix copyright year
71e466d173