Make the Manage Integrations Button defer scalar auth to the manager

This moves the responsibility of creating a URL to open from the button (and other components) to the integrations manager dialog itself.

By doing this, we also cut down on scalar API calls because we don't pick up on account information until the user opens the dialog.

res/css/views/settings/_IntegrationsManager.scss

@@ -29,3 +29,16 @@ limitations under the License.
     width: 100%;
     height: 100%;
 }
+
+.mx_IntegrationsManager_loading h3 {
+    text-align: center;
+}
+
+.mx_IntegrationsManager_error {
+    text-align: center;
+    padding-top: 20px;
+}
+
+.mx_IntegrationsManager_error h3 {
+    color: $warning-color;
+}