PubSub for parity-js (#5830)

* PubSub Integration WebSocket

* PubSub Provider API

* Parity License and fix switch statement

* Minor fix: use parameter api

* Exclude subscriptionId return

* Unsubscribe parameters as array

* secureProvider API added

* isSecure check

* Refractor: Formatting in callback (no Promise)

* Tests for parityProvider

* Refractor: Formatting in callback (secure API)

* Updated transaction documentation

* Module instead of API-Names, Options always as array (e.g. empty)

'parity' instead of 'parity_subscribe' calls
params with empty array as options. If eth_subscribe includes empty array parity-core will send invalid request (eth api doesn't have options)

* Removed isSecure transport check, because APIs are configurable

* Refractor Provider API to single Pubsub

* Modify transport layer to have single identifier for subscriptions

* FIX: Display pubsub errors

* Discard Messages after unsubscribing

* Fix: display error normal messages correctly

* Simplified code, removed unnecessary pubsub methods

* trace_call API 2nd argument blockNumber, first whatTrace

https://github.com/paritytech/parity/wiki/JSONRPC-trace-module#trace_call

* Separate namespaces pubsub. eth, parity, net

* Keep error for messages from unsubscribed topics.

* Fix: Unsubscribe Promise

* Add Test: Unsubscribe promise resolved

* Fix: 'error' in params