I've been using Codiad for a year now and am very happy. It's open source and you can host it yourself so no cost to you if you own a webserver.
Mainly use it for web projects but sometimes also for python or C. The latter requires a second tab open with some SSH client but still like it more than paid services like C9
Maybe you could try codiad, its a self-hosted web based ide that you can open from your browser. It can be used with touchscreens. I would recommend buying a Bluetooth keyboard tho, because you will have more screen space then. Demo at http://codiad.com . Only downside is you will need a webserver with php.
I don't think so.
However, you can install something like http://codiad.com/ on the same box and add its URL to HA menu as an iFrame. But this can get a bit complicated with a SSL setup - iframes don't really like self certs.
Yes for webdevelopment I use mainly my chromebook. I host my own codiad instance (Open Source cloud IDE) and use Secure Shell Chrome plugin to connect to my server