Added failed_evaluations property to StudentProject model. This is used to store GradingRecords which state a fail for this project. It's a list because manual changes in GradingRecords might force multiple GradingRecords to state a fail. Also it needs to be clear which GradingRecords have been processed and with which grade_decision.

# use glob syntax.
syntax: glob

*.pyc
*.zip
*~
.project
.pydevproject
app.yaml
build
tests/coverageResults
*,cover
tests/.coverage
*.git
*.egg-info
eggs
parts
.installed.cfg
bin
develop-eggs
.gitignore
.DS_Store
.settings