bug 867606 add data dictionary

This adds a data dictionary that describes breakpad data and the transforms
applied by things like the Processor in Socorro.

Also cleaning up some stray sqlalchemy files no longer needed.
Merge pull request #1216 from selenamarie/bug867606-data-dictionary

Bug867606 data dictionary
Merge pull request #1218 from erikrose/nose-1.3.0

Pick a more recent version of nose.
Add pip-cache to gitignore.

This is showing up in my socorro dir after running `make virtualenv` or something.
Add .DS_Store and "build" to gitignore.