Atlas generation refactoring

[adamltyson]

• Create validator script to ensure packaged atlas meet certain criteria (maybe also with an option to display images for a visual check?) #217
• Add checksum for packaged atlas #216
• Add a git commit hash metadata entry (also dependency version) [Feature] Remember code and dependency versions when generating atlas. #228
• Fix all broken atlas scripts (based on existing issues or validator failures) #218
• Refactor scripts to simplify code base as much as possible #219
• Add new atlases (based on issues, or community feedback) #221
• Possibly move quick validation checks into the atlas API #220
• Remove problematic dependencies (e.g. allensdk) #222
• Speed up atlas generation (or parallelise) so all scripts can be run automatically in a reasonable time frame (<24 hours). Could also be a slurm array job? #223

[adamltyson]

Closing this, because I'm not sure how useful this meta issue is, when the individual issues aren't very related.