add rake tasks to purge temp files, add to schedule.rb

[c4ssio]

• from deleted or long-inactive jobs
  • temp google sheets
  • temp gridfs files
  • temp local files
  • temp ssh files
  • temp hive tables
• from /tmp
  • anything older than 3 days

[c4ssio]

Instead, writing documentation for where the files are stored -- purging is too aggressive at this point.