Currency package update (#247)

* Initial currency overhaul before service system implementation

* Remove redundant currency string in orderbook.Base
Unexport lastupdated field in orderbook.Base as it was being instantiated multiple times
Add error handling for process orderbook

*  Remove redundant currency string in ticker.Price
 Unexport lastupdated field in ticker.Price
 Add error handling for process ticker function and fix tests

* Phase Two Update

* Update translations to use map type - thankyou to kempeng for spotting this

* Change pair method name from Display -> Format for better readability

* Fixes misspelling and tests

* Implement requested changes from GloriousCode

* Remove reduntant function and streamlined return in currency_translation.go

* Revert pair method naming conventions

* Change currency naming conventions

* Changed code type to exported Item type with underlying string to reduce complexity

* Added interim orderbook process method to orderbook.Base type

* Changed feebuilder struct field to currency.Pair

* Adds fall over system for backup fx providers

* deprecate function and children and fix linter issue with btcmarkets

* Fixed requested changes

* Fix bug and move mtx for rates

* Fixed after rebase oopsies

* Fix linter issues

* Fixes race conditions in testing functions

* Final phase coinmarketcap update

* fix linter issues

* Implement requested changes

* Adds configuration variables to increase/decrease time durations between updating currency file and fetching new currency rates

* Add a collection of tests to improve codecov

* After rebase oopsy fixes for btse

* Fix requested changes

* fix after rebase oopsies and add more efficient comparison checks within currency pair

* Fix linter issues

websocket.go

@@ -438,7 +438,13 @@ func wsGetExchangeRates(client *WebsocketClient, data interface{}) error {
 	wsResp := WebsocketEventResponse{
 		Event: "GetExchangeRates",
 	}
-	wsResp.Data = currency.GetExchangeRates()
+
+	var err error
+	wsResp.Data, err = currency.GetExchangeRates()
+	if err != nil {
+		return err
+	}
+
 	return client.SendWebsocketMessage(wsResp)
 }