fix: ws server terminate subscriptions when connection is closed by the client. (#483)

* fix: server should not send to closed subscription

Closing #481

* add a test

* rewrite me

* remove faulty server close

* fix tests

* fix tests

* remove needless code

* Update ws-client/src/client.rs

* fix: remove atomic flag; use `close_sender`

* remove terminate message; use close channel

* remove faulty subscription closed error msg

* fix tests

* fix grumbles

* fix build