This change makes invalidation mechanism more aggressive. With a primary goal to invalidate short living nodes faster. In current setup any node that became known in terms of discovery will stay in this state until it will fail to respond to 5 queries. Removing them earlier from a table allows to reduce latency for finding required nodes.
The second change, one adds a version for discovery, separates status dht from ethereum dht.
After we rolled out discovery it became obvious that our boot nodes became spammed with irrelevant nodes. And this made discovery process very long, for example with separate dht discovery takes ~2s, with mutual dht - it can take 1m-10m and there is still no guarantee to find a max amount of peers, cause status nodes is a very small part of whole ethereum infra.
In my understanding, we don't need to be a part of ethereum dht, and lower latency is way more important for us.
Closes: #941
Partially closes: #960 (960 requires futher investigations on devices)
* Rebase on 1.8.5
* Remove outdated patches and apply all others
* Use shh_post that returns hash
* Use bloom filter for request to mailserver
* Remove tests for sending messages without subbing first
* Fix deadlock in ethdb
* Expect null if receipt is not yet created
* Subscribe to messages before sending them in whisper test
