Use cls instead of self for class methods

Python convention is to use "cls" for class methods
and to use "self" for instance methods.
Slight style changes to test data loading.
Update version of AppEngine used by Travis.
Return a error message instead of throwing a 500 (fixes #360)

If the user provided bad input, a 500 error would be thrown
since some variables weren't defined. Instead, we now return
a JSON object with a simple error message.
Merge pull request #748 from legoktm/cls

Use cls instead of self for class methods
Merge pull request #749 from legoktm/360

Return a error message instead of throwing a 500 (fixes #360)
Changes to hopefully reduce flakiness of EventTeamUpdater tests.
Exclude one flaky test from Travis.
Merge branch 'master' of github.com:gregmarra/the-blue-alliance
Validation helper with tests
Merge pull request #750 from brandondean/validation-helper

Validation helper with tests