UI server refactoring (#5580)

* Full API in Authenticated WS server.

* Replacing UI server with Hyper.

* Solving CLI, RPCs and tests.

* Porting signer tests.

* Fixing origin recognition for dapps/rpc.

* Fixing tests. Adding parity-rpc-client to test.

* Dapps exposed as RPC method.

* JS code to support new connection scheme.

* Fixing dapps tests.

* Updating allowed origins/hosts to support web3.site.

* Fixing tests, fixing UI.

* Fixing tests.

* Removing invalid tests.

* Fixing merge.

* 404 fallback for UI

* Improve ContentFetcher constructor readability.

* Naming.

* Update .gitlab-ci.yml

fix CI lint error

* Fixing tests and linting issues.

* Fixing new tests.

* UI hosts.

* Submodules fix.