Small changes to make it so hterm works better in IE.  There are still some
issues around cut-copy-paste.

Also exposes terminal's pref_ object in a getter, and has the terminal pass
itself in the callback in the runCommandClass method.  This makes it so
integrating code doesn't have to directly access what looks like a private
variable.

Also fixes issue with double pasting the text with ctrl-v.  This was happening
because we are now listening for textInput events on the document body, rather
than just the x-screen.  The pasteInput text area would propagate a textInput
event up.  We are now catching this and stopping it.

Change-Id: I4c48f65cfc95cbd185083ea54f387229c76be983
Reviewed-on: https://chromium-review.googlesource.com/197372
Reviewed-by: Robert Ginda <rginda@chromium.org>
Tested-by: Robert Ginda <rginda@chromium.org>
hterm 1.37, nassh 0.8.27.2, double-paste fix, ie compat.

* Fix double-paste issue introduced in hterm 1.36.
* First round of IE compatibility fixes.

* Update nassh to 0.8.27.2.

Change-Id: I8437ef2f7128a831a6df25ada787cb693a3017b5
Reviewed-on: https://chromium-review.googlesource.com/197516
Reviewed-by: Robert Ginda <rginda@chromium.org>
Tested-by: Robert Ginda <rginda@chromium.org>