terminal.js:  Added "GateOne.Input" to the list of SuperSandbox dependencies.
gateone.js:  Improved `GateOne.Utils.showElement()` and `GateOne.Utils.hideElement()` so that they do a better job preserving an element's original 'display' style.
utils.py:  Added a `touch()` function.  This function is now being used in gateone.py for various things.
utils.py:  Updated `check_write_permissions()` to always return True if the user being checked is root.
utils.py:  Added support for capital "M" to indicate months in `convert_to_timedelta()`.
utils.py:  Added `kill_session_processes()` which will kill all processes associated with a given session.
gateone.py:  Fixed some bugs related to logging:  Missing log files are now automatically created and setting `--logging=none` works properly.  This should take care of the problem mentioned in issue #308 (https://github.com/liftoff/GateOne/issues/308).
gateone.py:  Added a new global function to cleanup old session directories:  `cleanup_old_sessions()`.
gateone.py:  Added a new global function that calls the new `cleanup_old_sessions()` and the regular `cleanup_user_logs()`:  `clean_up()`.
gateone.py:  Renamed the `user_logs_cleanup_interval` setting to just `cleanup_interval` since it now controls how often the user logs are checked *and* how often old sessions are checked.
auth.py:  Added a try/except block to the code that sends a message to the user indicating they're unauthorized to catch the edge case where the user disconnected the WebSocket before that message can be sent.  Really just prevents a cosmetic exception from appearing in the logs.
go_async.py:  Fixed a bug in `AsyncRunner.shutdown()` which could crop up if a subclass never completed calling its `__init__()` function before the instance was removed and garbage collection took place.  This should correct issue #310 (https://github.com/liftoff/GateOne/issues/310).
terminal_input.js:  Fixed xterm mouse support.  You can now click without having to select text in the process (LOL, what a strange bug).  It will also disable the native context menu but you can override this by holding down the alt key and clicking.  This should resolve issue #306 (https://github.com/liftoff/GateOne/issues/306)
terminal_input.js:  xterm mouse support now works with the scroll wheel!  Hold down the alt key to scroll normally instead (may be running into a browser bug here--sometimes it doesn't work--no logical reason why other than the browser doesn't like to scroll when alt is held sometimes).  This should (hopefully) make the person that reported issue #306 *extra* happy :)
gateone.py and app_terminal.py:  The old `options.dtach` quitting-time stuff from gateone.py was moved to app_terminal.py in the form of a new `quit()` function that is decorated with the `@atexit.register` decorator (man I love that thing!).
Bookmarks plugin:  Tweaked the CSS so the edge of the star (in the background of the bookmarks panel) doesn't get cut off.