playback.js:  Fixed a typo on line 390 that was causing mostly unimportant exceptions to show up in the JS console under certain circumstances.
gateone_misc.js:  Added `GateOne.i18n.gettext()` to the globally-exported shortcuts.
app_terminal.py:  Fixed a bug that would result in a harmless exception being logged if the user clicked the "Generate Sharing ID" button in the Share Terminal dialog before actually sharing anything.
app_terminal.py:  Fixed a bug in `TerminalApplication.detach_shared_terminal()` where you'd get an exception turning off terminal sharing for any given terminal.
terminal.js:  Fixed a typo that was causing terminal sharing to fail in Firefox.
Terminal Colors:  Brightened the "Bright" white foreground and background colors a bit to differentiate them from plain white.  This should resolve issue #192 (https://github.com/liftoff/GateOne/issues/192).
Dockerfile:  Updated to work with Docker's automated build mechanism so the liftoff/gateone repo shows up as "Trusted".  Also added a README.md so that the repo detailed description stays up-to-date.  Also added psutil to the pip install list since it's a dependency of the forthcoming X11 app.
gateone.js:  Added a callback option to the `GateOne.User.listUsers()` function.  Mostly because it makes it easier to debug.