Fix ValidationError import for MongoEngine 0.8

It moved from base to errors.
Merge pull request #1 from datalogics-kam/fix-validation-error

Fix ValidationError import for MongoEngine 0.8
Correct install_requires to capitalize Flask-WTF correctly.

The incorrect capitalization was causing problems with Buildout pinning
a version, because it disagreed with the package name on PyPI.
Merge pull request #2 from kam/fix-flask-wtf-requires

* kam/fix-flask-wtf-requires:
  Correct install_requires to capitalize Flask-WTF correctly.