Added extra quality notes from todays meeting.

For review @etorreborre @charleso @raronson @blever .

This is basically what we discussed today + the ones that I already had + a couple of extra testing ones that come up tonight.

I would ideally like to see this list continue to evolve, and ideally it would be a bit smaller, but the basic premise of a list like this is:
 - We write down the things most important to us right now.
 - Every week (or couple of weeks) do a quick review for progress on these areas.
 - Hopefully the core practices become ingrained in how we produce code in general and we remove the (now) obvious ones, and add new ones we can make real progress on doing better with.

Let me know if you have any thoughts, or better wording.
I would like each file to be have the same name as the main Scala class in it. This helps with navigating from compiler error messages to code with IDEs. For example there are 2 mr.scala files containing different classes (in `ingest` and `extraction`).