Added reversed for proof-of-stake syncing (#3092)

* reverse sync slow but working

* progress

* p

* close request

* backwards refactoring

* cleanup 1

* added RequestAssembler

* remove trash code and spaghetti

* efficient

* fix

* refactor

* tf

* refact

* final refactoring

* headers forward restored

* test fixed

* make CI happy

* resolved comments

* not using insertList anymore

* oops

* better collectors

* removed debug config

* avoid pointers

* added sleep

* use of channels

* sleeping

* added logs for ETL

* added more cleanup

* correct glacier

* some refactoring

* maxRequests

* tweaks

* config.go

* config conflicts

* renamed functions