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

gctrpc/rpc.swagger.json

@@ -840,6 +840,62 @@
         ]
       }
     },
+    "/v1/gethistoriccandles": {
+      "get": {
+        "operationId": "GetHistoricCandles",
+        "responses": {
+          "200": {
+            "description": "A successful response.",
+            "schema": {
+              "$ref": "#/definitions/gctrpcGetHistoricCandlesResponse"
+            }
+          }
+        },
+        "parameters": [
+          {
+            "name": "exchange",
+            "in": "query",
+            "required": false,
+            "type": "string"
+          },
+          {
+            "name": "pair.delimiter",
+            "in": "query",
+            "required": false,
+            "type": "string"
+          },
+          {
+            "name": "pair.base",
+            "in": "query",
+            "required": false,
+            "type": "string"
+          },
+          {
+            "name": "pair.quote",
+            "in": "query",
+            "required": false,
+            "type": "string"
+          },
+          {
+            "name": "rangesize",
+            "in": "query",
+            "required": false,
+            "type": "string",
+            "format": "int64"
+          },
+          {
+            "name": "granularity",
+            "in": "query",
+            "required": false,
+            "type": "string",
+            "format": "int64"
+          }
+        ],
+        "tags": [
+          "GoCryptoTrader"
+        ]
+      }
+    },
     "/v1/getinfo": {
       "get": {
         "operationId": "GetInfo",
@@ -1548,6 +1604,35 @@
     "gctrpcCancelOrderResponse": {
       "type": "object"
     },
+    "gctrpcCandle": {
+      "type": "object",
+      "properties": {
+        "time": {
+          "type": "string",
+          "format": "int64"
+        },
+        "low": {
+          "type": "number",
+          "format": "double"
+        },
+        "high": {
+          "type": "number",
+          "format": "double"
+        },
+        "open": {
+          "type": "number",
+          "format": "double"
+        },
+        "close": {
+          "type": "number",
+          "format": "double"
+        },
+        "volume": {
+          "type": "number",
+          "format": "double"
+        }
+      }
+    },
     "gctrpcCoin": {
       "type": "object",
       "properties": {
@@ -2032,6 +2117,17 @@
         }
       }
     },
+    "gctrpcGetHistoricCandlesResponse": {
+      "type": "object",
+      "properties": {
+        "candle": {
+          "type": "array",
+          "items": {
+            "$ref": "#/definitions/gctrpcCandle"
+          }
+        }
+      }
+    },
     "gctrpcGetInfoResponse": {
       "type": "object",
       "properties": {