clear out thumbnail target; add pid to tempfile (#1104)
Videocheck utility, replacing rekelvin command (#935)

From help text:
   Audit videos to see what commands need to be run to fix them
   out.  Looks out for missing thumbnails or smaller video files.
   Does this by comparing contents of database to what is in S3.
   Note that this doesn't do any *semantic* validation, just checks
   for presence of files.  For example, doesn't tell if they are
   good thumbnails, or even the right thumbnails, just that there
   are thumbnails.

Complete rewrite of the "rekelvin" command so it is now a much more
thorough audit.
- compares DB contents to what is in S3.  Before we would get lots of
  spurrious errors from junk lying around in S3, now we start with the
  DB as authority and then figure out what needs to be cleaned up based
  on that.
- looks for missing small or large video sizes
- renamed commands so they're a little more clear

Prior command would automatically kick off jobs, which was scary and
hard to control reliably (--max, --delay, etc).  Now just dump out a set
of commands to run and the user can do with those what they will: pipe
to xargs, run one at a time, etc.
Fix cmd name in help text; default to remote (#935)

We pretty much never want to kelvinate locally, unless we are testing.
Even if you're kicking off from a util machine, good form to go through
the celery queue.  So default to remote.
Narrow help text (#935)
str(video_id) in initializer instead of casting throughout (#935)
Print missing video assets too (#935)

Those are almost the most serious errors, print those out too even
though there is no "command" to fix.
Merge branch 'master' of github.com:Stanford-Online/class2go into sef-sprint-17-video
Go back to old cmd name (kelvinate) (#935)
Merge branch 'master' of github.com:Stanford-Online/class2go into sef-sprint-17-video
Merge branch 'master' of github.com:Stanford-Online/class2go into sef-sprint-17-video
Kelvinator refactor and bug fixes (#1104)

Fundamental algorithm is the same, this is a bunch of bug fixes and
general cleanups, long overdue.

Bug fixes
- add pid to end of temp directory since it wasn't unique.
- clean up temp directory after errors.  Observe now that there are many
  left-behind work directories

Features
- added notification - now when done, it can send a recap mail.  Not
  intended for normal use, but could be useful for cleanups or misc.
  debugging.
- got local mode working again
- infer local or remote mode by what's in your database.py, but new
  options to override

Code improvements
- split one big function into a set of more reasonable small ones
- variables now underscore delimited (test_word) instad of camel
  (testWord)
Fix up file nameing for remote kelvination (#1104)

Since we're going through boto to get video files now, instead of
download directly from s3,
- don't need to prepend bucket into file name (good)
- don't need to hardcode S3 location (good)
- much simpler (good)
Fix file name in debugging stmt (#1104)
Add resize command and utility (#1052)

Resize uses ffmpeg, much like kelvinator, to create large and small
versions of the video file.  Involved a bunch of factoring of shared
functions from kelvinator into utility.py.

Still to do:
- test from celery and s3 (works locally)
- consider parameterizing the presets (large/small and their values), no
  reason to be hard coded
- the video settings aren't right -- actually doesn't make any smaller
  just yet.
Try smaller sizes, still not much savings (#1052)
Kick off resizing jobs from video upload (#1052)
Standardize on codec options; parameterize (#1052)
Merge branch 'master' of github.com:Stanford-Online/class2go into sef-sprint-17-video
Fix typo in import (#1104)
Fix "small" size to 640x360 (#1104)