A bunch of changes and fixes

[lexqt]

Hello, @wpjunior.

Maybe I misunderstood something from your mail (whether a new version will be introduced in a current mongotools repo or in some external system only) but anyway I created this pull request just in case.

A bunch of changes and fixes intended to make mongotools views and forms more like their equivalents from Django (v 1.4) and to support more features from MongoEngine (v 0.7-0.8), e.g.:

• Sync mongotools codebase with Django 1.4
• Add missed view and form classes properties
• Use inheritance from Django classes whenever it's possible
• Rename MongoForm to DocumentForm (like in https://github.com/jschrewe/django-mongodbforms)
• Add EmbeddedDocument form
• Fix FileField support
• Fix form validation
• etc