Add mixin to check access rights client-side.

This replaces the Vuex getters approach (writeaccess, adminaccess)
which, as access rights are no longer global but dependent on each
project's settings, are no longer appropriate.

lib/www/client/source/src/mixins/access.js

@@ -0,0 +1,31 @@
+import { mapGetters } from 'vuex';
+import access from '@/lib/organisations/access';
+
+export default {
+  name: "AccessMixin",
+
+  computed: {
+    ...mapGetters(['user', 'projectConfiguration'])
+  },
+
+  methods: {
+
+    access (operation, item) {
+      if (!item) item = this.projectConfiguration;
+
+      return access(this.user?.organisations ?? {}, item?.organisations ?? {}, operation);
+    },
+
+    readaccess (item) {
+      return this.access('read', item);
+    },
+
+    writeaccess (item) {
+      return this.access('write', item);
+    },
+
+    adminaccess (item) {
+      return this.access('edit', item);
+    }
+  }
+}