Backports to beta (#1919)

* RPC errors & logs (#1845)

* Refactoring errors in RPC

* Updating jsonrpc-core

* Fixing code_at

* Avoid mentioning obvious segments in proof

[ci:skip]

* fixed cache_manager lock order

* Purging .derefs, fixing clippy warnings. (#1890)

* Fixing clippy warnings

* Purging derefs

* Simplifying engine derefs

* Simplifying more engine derefs

* Adding more details to miner log

* fixed #1889, .DS_Store is no longer treated as key file (#1892)

* fixed #1889, .DS_Store is no longer treated as key file

* ethstore filters directories, hidden files and common system files

* fixed compiling

* fix regression with geth dir

* fix regression with geth dir

* Fix ipc compilation and add ipc feature to test targets (#1902)

* fix compilation and add it to the ci run

* no separator?

* use quotes and spaces

* RocksDB version bump

* Don't return deleted nodes that are not yet flushed (#1908)

* polling & connection timeouts (#1910)

* Peers RPC + UI displaying active/connected/max peers (#1915)

* Peers API

* Bumping Parity-UI

* Fixing tests

* Save nodes removed from backing_overlay until commit (#1917)