Revised subcond, params, & content presentation

1. Formerly, parameters were assigned in two different places: in
assign_parameters.php and in content.js. Now, assign_parameters.php is
replaced with assign_subcondition.php, which ONLY assigns subcondition.
All other parameter assignments are now handled in index.html.

2. subcondition now counterbalances 3 parameters instead of 2:
question_order, answer_order, and term_consistency, the last one being a
new addition.

3. added database submit for running online but not on turk

4. extensively revised organization of content.js, the main point being
to better separate trial spec generation, now in getTrialSpecs, and
presentation of trials, now in displayButtonChoice. The latter contains
little or nothing specific to the content of this exp.