UI improvements

[felixbinder]

• We should include a more salient visual cue (other than the Next button being clickable) when the experiment will allow participants to move onto the next trial.
• We should include a trial counter in one of the corners of the display to tell participants exactly how many trials remain.
  Nice-to-have:
• We may want to consider making the buttons and button text size larger (shared CSS file across all tasks), and
• Yes/ No spelled out in all CAPS.
• We may want to use a neutral gray background (similar in hue/value to the appearance of the walls in the video) to reduce the jarring/slightly distracting effect of the abrupt disappearance of the scenarios prior to the decision.