Gemini: Fix pair handling and upgrade websocket connection for public market data (#644)

* Fix Gemini pairs

* Overhaul websocket for marketdata v2

* Code cleanup + returns

* Address shazbert's and glorious's nits

* Go mod tidy

testdata/http_mock/gemini/gemini.json

@@ -2135,8 +2135,16 @@
     {
      "data": [
       "btcusd",
+      "btcdai",
+      "btcgbp",
+      "btceur",
+      "btcsgd",
       "ethbtc",
       "ethusd",
+      "ethgbp",
+      "etheur",
+      "ethsgd",
+      "ethdai",
       "bchusd",
       "bchbtc",
       "bcheth",
@@ -2148,7 +2156,34 @@
       "zecbtc",
       "zeceth",
       "zecbch",
-      "zecltc"
+      "zecltc",
+      "batusd",
+      "batbtc",
+      "bateth",
+      "linkusd",
+      "linkbtc",
+      "linketh",
+      "daiusd",
+      "oxtusd",
+      "oxtbtc",
+      "oxteth",
+      "filusd",
+      "ampusd",
+      "paxgusd",
+      "compusd",
+      "mkrusd",
+      "zrxusd",
+      "kncusd",
+      "storjusd",
+      "manausd",
+      "aaveusd",
+      "snxusd",
+      "yfiusd",
+      "umausd",
+      "balusd",
+      "crvusd",
+      "renusd",
+      "uniusd"
      ],
      "queryString": "",
      "bodyParams": "",