Evan/remove front bias sampling

[uoefeb]

Most important change: is sampling_scripts/frame_picker.py which does the following:

if there are more than 6 scenes:
  pick 1 frame from 6 random scenes

if there are 6 scenes:
  pick 1 frame from each scene

if there are less than 6 scenes:
  pick on frame from all scenes, and then fill the remaining deficit from frames selected randomly from all scenes

→ then sort the frames by order

Additionally:

• I've imported frame_picker.py to all the sampling scripts to force them to use the same random seed
• I've made the pyscene script print the exceptions it runs into (while testing this I needed it)

[uoefeb]

I'm going to go ahead and merge this. Please feel free to leave comments on it after the fact, and I can revisit them to make fixes, etc.