Add email settings management UI

[hikalkan]

• We can add a setting management UI tab for "Email" to see and change the email settings. Add it directly to the open source setting-management module.
• This requires to add application and httpapi (and you know, some other) projects to the setting-management module. application layer will depend on the Volo.Abp.Emailing package as you can understand.
• Then we add a "settings" page to the application startup template which contains a single "Email" tab. It also will be available for the abp commercial startup template, automatically.