use webview or iframe?

[PerBothner]

Depending on the usingWebview variable, atom-domterm can use either a <webview> or an <iframe> for the embedded terminal emulator. Currently, it works better with <iframe> (usingWebview is false), so that is the default. The main problems with using <webview> are:

1. Serialization with <webview> isn't working - which causes lots of problems. I don't know why - it could be related to the DomTermView class not extending View. (I haven't figured out how to do that in plain JavaScript.)
2. The Atom keybindings override DomTerm's handling of key events. Given that a terminal emulator needs to handle most keybindings on its own, this is a problem. The keymaps/domterm.cson file fixes some of the problems, but it would be better for the default to be native. (I can't get native-key-bindings to work.) Using an <frame> handles this by default.

On the other hand, there are some things using <webview> with node integration handles better than <iframe>. I've been fixing various <iframe> problems but it seems to be fighting the system.