Websocket connection handling and subscription management (#297)

* Step one: Sets up  connection handler for websockets to always be connected until a shutdown event is received.
Sets up a vague subscription handler to ensure subscriptions are subscribed

* Adds support for resubscriptions for bitfinex, bitstamp, bitmex and btcc. Adds subscription params for special websocket subscription requirements. Removes subscription monitor from wait group so that it can exist despite a shutdown and continuously check

* Adds channel subscription support to bitmex, btse, coibasepro, coinut, gateio, gemini, hitbtc, huobi, hadax, kraken, okgroup, poloniex and zb

* Implements unsubscribe for bitfinex, btcc, btse, coinbasepro, gateio, gitbtc, huobi, hadax

* ManageSubscriptions now called from WSConnect and made private instead of inside individual exchanges. ManageSubscriptions can now unsubscribe. exchange_websocket_types.go now contains all exchange_websocket.go types to avoid clutter

* Adds it to websocket functionality so managesubscriptions will close when not supported

* Separates functions into testable functions to ensure logic works. Adds tests. Updates websocket setup to include verbosity (inherited from exchange). Adds no connection tolerance to fatal on failed reconnects

* More exchange_websocket tests. Updating to use pointers. Creation of equals func to make comparison easier

* Fixes okex, okcoin tests. Fixes race conditions. Removes pointer usage again.

* Adds subscribe and unsubscribe to wrappers

* Fixes deadlock. Fixes ws verbosity.

* Updates all exchanges to properly support subscription/connection feature. Also reintroduces race conditions....

* Moves connection varialbes to struct from package to allow each websocket to have their own reconnection checks. Neatens up logs

* Fixes lint/critic issues. Fixes tests. Removes unused function.

* Moves websocket ratelimiter to their own const variables. Fixes more race conditions with connecting variable

* Removes redundant subscribe functions. Ensuring only the exchange_websocket.go can manage subscriptions. Fixes debug logs to be verbose wrapped

* Fixes issue with slice copying. Re-adds okgroup default channels

* Adds nolint to append

* Adds comments and adds support for gateio auth request subscriptions

* Adds new test to ensure slices dont point to the same vars

* removes fatals. gofmt goimports

* more gofmts

* Addresses PR comments, removing empty and redundant lines

* Addresses PR comments. Ensures that writing to the websocket is single-threaded by adding a mutex to exchanges. Minimises wrapper code and moves subscription loops to exchange_websocket. Privatises ChannelsToSubscribe, Connecting properties and removeChannelToSubscribe func to prevent unnecessary tampering.

* Removes unused mutex. FMTS and IMPORTS

* Fixes request lock time change

* More specific logs

* Renames ws mutex. Fixes bitmex subscriptions. Increased gateio ratelimiter to 120ms. Removes ratelimiter from bitfinex, bitmex, bitstamp, btcc, btse, coibasepro, hitbtc, huobi, hadax, poloniex and zb

* changes recieved typo due to not being well received

* Fixes parsing issue with Huobi and hadax

* Fixes data race with more locks

* removes defer locks. fixes huobi/hadax verbose output

* Fixes double JSONEncode for coinut. Fixes verbose output for coinut

* gofmt,goimport for coinut

* Fixes issue where multiple connection monitors can spawn

* Removes defer exchange.WebsocketConn.Close() in defer handledata exit as connectionmonitor handles connections instead

* gofmt and go import

* More fmts

testdata/configtest.json

@@ -1085,7 +1085,7 @@
    "name": "OKCOIN International",
    "enabled": true,
    "verbose": false,
-   "websocket": false,
+   "websocket": true,
    "useSandbox": false,
    "restPollingDelay": 10,
    "httpTimeout": 15000000000,