🎉 Add Nextcloud widget

Add a widget supporting the `capabilites`, `user`
and `serverinfo` Nextcloud APIs.

Basic branding, user and quota information is always displayed
and when the provided credentials are for and admin user then
server information is also displayed.

APIs:
* [capabilities](https://docs.nextcloud.com/server/latest/developer_manual/client_apis/OCS/ocs-api-overview.html#capabilities-api)
* [user](https://docs.nextcloud.com/server/latest/developer_manual/client_apis/OCS/ocs-api-overview.html#user-metadata)
* [serverinfo](https://github.com/nextcloud/serverinfo)

src/mixins/NextcloudMixin.js

@@ -0,0 +1,82 @@
+import { serviceEndpoints } from '@/utils/defaults';
+import { convertBytes, formatNumber, getTimeAgo } from '@/utils/MiscHelpers';
+// //import { NcdCap } from '@/utils/ncd';
+
+/** Reusable mixin for Nextcloud widgets */
+export default {
+  data() {
+    return {
+      capabilities: {
+        notifications: null,
+        activity: null,
+      },
+      capabilitiesLastUpdated: 0,
+    };
+  },
+  computed: {
+    hostname() {
+      if (!this.options.hostname) this.error('A hostname is required');
+      return this.options.hostname;
+    },
+    username() {
+      if (!this.options.username) this.error('A username is required');
+      return this.options.username;
+    },
+    password() {
+      if (!this.options.password) this.error('An app-password is required');
+      return this.options.password;
+    },
+    headers() {
+      return {
+        'OCS-APIREQUEST': true,
+        Accept: 'application/json',
+        Authorization: `Basic ${window.btoa(`${this.username}:${this.password}`)}`,
+      };
+    },
+    proxyReqEndpoint() {
+      const baseUrl = process.env.VUE_APP_DOMAIN || window.location.origin;
+      return `${baseUrl}${serviceEndpoints.corsProxy}`;
+    },
+  },
+  methods: {
+    endpoint(id) {
+      const endpoints = {
+        capabilities: `${this.hostname}/ocs/v1.php/cloud/capabilities`,
+        user: `${this.hostname}/ocs/v1.php/cloud/users/${this.username}`,
+        serverinfo: `${this.hostname}/ocs/v2.php/apps/serverinfo/api/v1/info`,
+      };
+      return endpoints[id];
+    },
+    fetchCapabilities() {
+      const promise = Promise.resolve();
+      if ((new Date().getTime()) - this.capabilitiesLastUpdated > 3600000) {
+        promise.then(() => this.makeRequest(this.endpoint('capabilities'), this.headers))
+        // //promise.then(() => NcdCap)
+          .then(this.processCapabilities);
+      }
+      return promise;
+    },
+    processCapabilities(data) {
+      const ocdata = data?.ocs?.data;
+      if (!ocdata) {
+        this.error('Invalid response');
+        return;
+      }
+      this.branding = ocdata?.capabilities?.theming;
+      this.capabilities.notifications = ocdata?.capabilities?.notifications?.['ocs-endpoints'];
+      this.capabilities.activity = ocdata?.capabilities?.activity?.apiv2;
+      this.version.string = ocdata?.version?.string;
+      this.version.edition = ocdata?.version?.edition;
+      this.capabilitiesLastUpdated = new Date().getTime();
+    },
+    formatNumber(number) {
+      return formatNumber(number);
+    },
+    convertBytes(bytes) {
+      return convertBytes(bytes);
+    },
+    getTimeAgo(time) {
+      return getTimeAgo(time);
+    },
+  },
+};