Remove half-implemented publish/subscribe system

Remove half-implemented publish/subscribe system

* Track blocks in flight by nodeid as well as block hash

Because we can re-request the same block via the request-manager
we need to also track blocks in flight by nodeid as well as hash.

We also need to be aware that when a block returns or when we
finalize the node that we only remove the block hashes from
mapBlocksInFlight for that specific peer.

* Move methods for handling mapBlocksInFlight

from requestManager.h into requestManager.cpp

* Remove QueuedBlock lookups from GetNodeStateStats

Instead lookup blocks in flight for this nodeid by using
the requestManager and mapBlocksInFlight.

* Remove QueuedBlock from FinalizeNode()

* Move QueuedBlock to the requestmanager

* Remove state from CheckForDownloadTimeout()

We no longer require state because we've moved the state we need
into the requestmanager. As a result we also do not need cs_main and
we can thus move the check for download timeout to before we take
the cs_main lock in SendMessages().

* Move nBlocksInFlight from nodestate.h to the requestmanager

This now allows us to completely move FindNextBlocksToDownload()
to the request manager but more importantly we can now remove
cs_main from MarkBlocksAsInFlight.

* Remove a nodesate from the requestmanager on FinalizeNode()

* Cleanup and code simplification

* Simplify GetBlocksInFlight()

* Return false if pnode is null in MarkBlocksAsReceived()

* Lock cs_objDownloader in two other places

* use itInflight to check for nodeid count rather than a second lookup

* use an iterator to erase from mapblocksinflight

* use a temporary to avoid a dangling iterator

e7364ca Update for merging (Fuzzbawls)
4de4932 add snapcraft support to pivx, static build (cevap)

Pull request description:

  Re-submission of @cevap 's Pull request due to his account being closed.

  This adds the ability to do nightly snapcraft builds (released to the beta channel) via LaunchPad.

  Builds are published on the snapcraft store (https://snapcraft.io/pivx-core)

ACKs for top commit:
  random-zebra:
    utACK e7364ca
  furszy:
    utACK e7364ca
  Warrows:
    utACK e7364ca

Tree-SHA512: f4614c34d55100944b369333222217a9275f3fb87f985f4f7e34a33c03d4b3095b26d5c0b71427bfa71107579ea0b2c36a5375a287860f46e7d966acd27b8890