Added TFR, rvsd training exposition, rvsd css, etc.

- in experiment.js, added feedback to all questions, added TFR
questions, revised training exposition format to use that of exp 6,
added TFR training exposition, deleted background question about
visual/verbal style
- modified css to use larger font and area, changed jspsych-scmvar
accordingly
- set training plugin in jspsych-scmvar to let them go on after 4th
error
- modified demo.html interface to unify testing and regular run
functions, add testing dashboard, etc.
- revised mysql queries for counting completions in
assign_parameters.php
- revised debriefing