Remove using_sandbox from config

Instead, whether sandbox mode is in use gets passed as an argument to
the server subprocess and then down to the flask app. Seems to be
working but there are a bunch of files I changed here so some more eyes
would be good.

Right now shell just starts in sandbox automatically. We could change
that and turn the"always_launch_in_sandbox" config option into a
"launch_in_sandbox_or_live" type option, or just remove the option.
updating docs to reflect this change
Merge remote-tracking branch 'origin/dev' into modeify_server

Conflicts:
	psiturk/experiment.py
stepping version number due to change in config.txt file

the previous merge resolve the issue with the test failing
Add launch_in_sandbox_mode config option

Defaults to true. Replaces always_launch_in_sandbox option
Change docs for Shell Parameters config
Merge remote-tracking branch 'origin/modeify_server' into dev