Create exchange rate service , use CORS proxy for requests

app/services/exchange-rates.js

@@ -0,0 +1,29 @@
+import Service from '@ember/service';
+import { tracked } from '@glimmer/tracking';
+import config from 'kredits-web/config/environment';
+
+// Need to go through proxy for CORS headers
+const bitstampBaseUrl = `${config.corsProxy}https://www.bitstamp.net/api/v2`;
+
+async function fetchFromBitstamp(currencyPair) {
+  try {
+    const res = await fetch(`${bitstampBaseUrl}/ticker/${currencyPair}/`).then(r => r.json());
+    return res.vwap; // Last 24 hours volume weighted average price
+  } catch(e) {
+    console.error('Could not fetch exchange rate from Bitstamp:', e);
+    return 0;
+  }
+}
+
+export default class ExchangeRatesService extends Service {
+  @tracked btceur = 0;
+  @tracked btcusd = 0;
+
+  async fetchRates (source='bitstamp') {
+    switch(source) {
+      case 'bitstamp':
+        this.btceur = await fetchFromBitstamp('btceur');
+        this.btcusd = await fetchFromBitstamp('btcusd');
+    }
+  }
+}