Conformity to new Flask-WTF version

This version is compatible to the new version(s) of Flask-WTF.
Said new version dropped the html5 elements since html5 is now handled by WTForms itself.
However WTForms doesn't supply an EmailField, so I simply used a TextField.
Obviously, mails have no client-side validation now.

I also fixed a bug in the git extension that resulted in an uncaught exception on first commit.

I didn't run any tests, since I didn't see any.
Please proofread the changes.