Whisper cli (#8201)

* getting started

* wip wip

* add parsing of pool-size and enable panic-hook

* more cli options

* remove explicit unwrapping

* bump dependencies to parity-jsonrpc

* add tests

* remove tests

* bump jsonrpc

* Remove unused dependencies

* add logging to the cli

* Fix so `FilterManager` drops its resources

* Introduced an AtomicBool flag in FilterManager to cancel the `Decryption Worker Thread`
* Added some very basic test to faulty arguments

* ignore privileged port test