More UI suggestions

[AshiqKiron]

1. Move the Overview page to weMail menu, since currently weMail menu + overview menu perform the same page
2. Overview page - change + Add campaign to + Send Email
3. Add edit option in the “View, Delete, Delete” dropdown on the campaigns page.
4. Campaign->Design - Template Options dropdown isn’t necessary, since there’s only one option. Rename “Template Options“ to “Save Template”
5. Campaign->Design - Rename Save As Draft to Save Email
6. Campaign->Send - Rename Save As Draft to Save Email.
7. Campaign->Send - Rename Preview & Test Email to Send Test Email.
8. Show segment result without the need to save the segment.
9. Add “Back” button in 
wp-admin/admin.php?page=wemail#/import/mailerlite/
wp-admin/admin.php?page=wemail#/import/mailpoet
and in all importer pages
10. Redesign billing tab
11. Add back button - 
https://stagingwp.getwemail.io/wp-admin/admin.php?page=wemail#/integrations/e-commerce/wcommerce/woocommerce
https://stagingwp.getwemail.io/wp-admin/admin.php?page=wemail#/integrations/popup-forms/popup-maker
https://stagingwp.getwemail.io/wp-admin/admin.php?page=wemail#/integrations/contact-forms/fluent-forms
12. Add custom field options for subscribers
13. Integrations all option doesn’t look like it’s selected by default
14. Under Manage segments, edit option
15. Single subscriber page doesn’t have a back button