Add common CSS and components

[MAILPOET-2677]

assets/js/src/settings/components/index.ts

@@ -0,0 +1,5 @@
+export { default as Tabs } from './tabs';
+export { default as Label } from './label';
+export { default as Inputs } from './inputs';
+export { default as SaveButton } from './save_button';
+export { default as SegmentsSelect } from './segments_select';