I have a perfect solution for you that is already built is fully web based, can store your email list, supports importing , supports editing using a WYSIWYG(what you see is what you get) editor(that's what we call the editor you linked). The support team for the service is top notch, and the service is free until the list that you're sending to has over 2,000 users. once you hit that mark, they have both a monthly or flexible pay just for what you use payment system to keep costs low.
They have a mobile app as well which you can use to view the statistics on the emails you send, like how many people click your links, where in the world people are opening your emails from.
Emails can be scheduled in advance.
My proposition, I can build you a professional email template that matches your company's looks and allows you to easily edit it in said service and put out top quality emails to your clients/subscribers.
I design both Responsive and static email templates.
Responsive email templates adjust their layout to the screen size of the device they're being viewed on.
My history:
I worked at an advertising agency building and managing email campaigns building 3-4 email newsletters that would go out on a weekly basis to 15,000+ people.