Updated mrr stats on dashboard (#1847)

refs https://github.com/TryGhost/Team/issues/469

- Adds basic percentage growth stat for mrr on dashboard
- Adds base data for mrr chart in case of no mrr stats

ghost/admin/app/controllers/dashboard.js

@@ -50,13 +50,19 @@ export default class DashboardController extends Controller {
         this.membersStats.fetchMRR().then((stats) => {
             this.events.loading = false;
 
-            const currencyStats = stats[0];
+            let currencyStats = stats[0] || {
+                data: [],
+                currency: 'usd'
+            };
             if (currencyStats) {
                 currencyStats.data = this.membersStats.fillDates(currencyStats.data) || {};
                 const dateValues = Object.values(currencyStats.data).map(val => val / 100);
                 const currentMRR = dateValues.length ? dateValues[dateValues.length - 1] : 0;
+                const rangeStartMRR = dateValues.length ? dateValues[0] : 0;
+                const percentChange = rangeStartMRR !== 0 ? ((currentMRR - rangeStartMRR) / rangeStartMRR) * 100 : 0.0;
                 this.mrrStats.data = {
                     current: `${getSymbol(currencyStats.currency)}${currentMRR}`,
+                    percentChange,
                     options: {
                         rangeInDays: 30
                     },

ghost/admin/app/templates/dashboard.hbs

@@ -16,7 +16,7 @@
                     <div class="gh-dashboard-summary">
                         {{#if this.mrrStats.data}}
                             <div class="data">{{this.mrrStats.data.current}}</div>
-                            <div class="growth">0.0%</div>
+                            <div class="growth">{{this.mrrStats.data.percentChange}}%</div>
                         {{else}}
                             <div class="data">$0</div>
                             <div class="growth">0.0%</div>