Headers poc 5 - Intermediate (#1145)

* Add headers persistence

* Print flushBuffer

* Fix indexing problem

* Not skip hard-coded headers if the files are empty

* Fix lint

* print anchor state after init

* Properly construct file names

* Add check sub-command

* Fix lint

* Fix lint

* Fix lint

* Print more info when recovering

* Fix recovering

* Fix recovery

* Add anchors also as tips

* 2-level priority queue for tips

* Initialise tipQueue in anchor

* update maxTipHeight

* fix type

* Add anchors to the anchorQueue and rebuild anchorQueue on deletion

* Fix NPE

* fix recovery

* User buffersize, add hard coded headers to buffer

* Reinit anchorQueue

* Schedule requests after recovery

* No fix

* Remove duplicates

* Report duplicate headers

* Log buffer additions

* Fix for duplicate headers

* Try to fix duplicate headers again

* remove TODO comment

* Use LLRB instead of heap for anchors

* Print reserveTip info

* Correctly replace anchors in the tree

* Remove excessive logging

* Print tips attached to the anchor

* Print tips better

* limitTips instead of reserveTip

* Print forked headers

* Use pointers in llrb

* Print tipStretch

* Print limitTips

* Mininise AnchorItem

* Put anchors into the tree

* Fix totalDiff calculation, but is it needed?

* Remove totalDifficulty from anchors

* CheckInitiation

* Fix tests

* Fix lint, print more at check initiation

* Better output for hard-coded anchors

* Print hard-coded anchors better

* Prioritise anchors with short stretches

* Prioritise by chainSize

* Use linked list instead of heap for requestQueue

* Fix problem of no requests

* Push front

* Fix lint

* Not verify PoW for too far in the past and future

* Fix Calculation of totalDifficulty when Connect

* Fix hard tips

* Another fix for tips