Add OHLC retrieval func (GetHistoricCandles) to all exchanges and expose it as a wrapper func (#414)

* initial wiring to providegethistoricalcandles

* initial wiring to providegethistoricalcandles

* initial wiring to providegethistoricalcandles

* gethistriccandles work from cli using hard coded inputs

* gethistoriccandles RPC service and CLI working fine for coinbasepro

* fixed unit test

* input check on grpc for gethistoriccandles

* updated deps

* fixed the return value when a method is not yet implemented

* code review: fixed CLI input check and int32->int64

* code review: handling wrong exchange name

* added check on granularity and allowing start and end being empty

* code review: removed currency2

* code review: dependency reverted

* improved func comment

* typo in func comment

* get historic values tests

* unit tests for get historical rates on coinbasepro

* using time format time.RFC3339

* names to camel case and improved comments

* test cleanup

* changed to camel case

* added InArray tests

* dropped not needed string time

* enforced use of int64

* fixed make check

* cleaned up code organisation to be consistent

* fixed Travis remarks

* more Travis remarks

* added comments

* regenerated proto files after merge

* linter fix

exchanges/protocol/features.go

@@ -37,4 +37,5 @@ type Features struct {
 	AuthenticatedEndpoints bool `json:"authenticatedEndpoints,omitempty"`
 	MessageCorrelation     bool `json:"messageCorrelation,omitempty"`
 	MessageSequenceNumbers bool `json:"messageSequenceNumbers,omitempty"`
+	CandleHistory          bool `json:"candlehistory,omitempty"`
 }