toolkitpromise-992309: Copy promise.jsm to promise.js

Updated to work on the web.
No need for mozilla review.

Signed-off-by: Joe Walker <jwalker@mozilla.com>
toolkitpromise-992309: Switch to ES6 API

s/promise.defer/new Promise/g

Signed-off-by: Joe Walker <jwalker@mozilla.com>
commandappears-983865 Opacity allows clicks, use visibility

Signed-off-by: Joe Walker <jwalker@mozilla.com>
commandappears-983865: Fix text mode help

This is not strictly part of fixing bug 983865, but the changes to m-c
are trivial, so I'm including it there.

'gcli help' failed on the command line because there wasn't a good way
to generate a DOM to format the string output from the help command.

This moves the toDom function from util to host, so we can have a tweak
to use jsdom when there is no document available.

Signed-off-by: Joe Walker <jwalker@mozilla.com>
l10n-1020222: Remove unused l10n strings

Signed-off-by: Joe Walker <jwalker@mozilla.com>