[WIP] Integrate header download with stage 1 (saving headers to the database) (#1330)

* move locking to the hd object itself, create ready channel

* Fix lint

* More integration

* Fix lint

* Connect to processing

* Set hd.files at recovery

* Serialise processSegment

* Fix lint

* Not prepend filesDir

* Write to the database

* Fix lint

* Set up genesis block

* Fix hard coded tips

* Fix chainbreak false alarm

* Recover from DB

* Skip non-header records

* Not initialise if recovered from DB

* Fix lint