Please backport wtforms 2.1-1 (universe) from xenial

[Frédéric Bonnard]

Please backport wtforms 2.1-1 (universe) from xenial to trusty.

Reason for the backport:
========================
To be able to run https://github.com/NVIDIA/DIGITS on trusty, a few packages
are needed as dependencies for https://github.com/miguelgrinberg/Flask-SocketIO
which itself is needed by DIGITS.

Testing:
========
Mark off items in the checklist [X] as you test them, but please leave the checklist so that backporters can quickly evaluate the state of testing.

You can test-build the backport in your PPA with backportpackage:
$ backportpackage -u ppa:<lp username>/<ppa name> -s xenial -d trusty wtforms

* trusty:
[X] Package builds without modification
[X] python-wtforms-doc installs cleanly and runs
[X] python-wtforms installs cleanly and runs
[X] python3-wtforms installs cleanly and runs

Reverse dependencies:
=====================
The following reverse-dependencies need to be tested against the new version of wtforms. For reverse-build-dependencies (-Indep), please test that the package still builds against the new wtforms. For reverse-dependencies, please test that the version of the package currently in the release still works with the new wtforms installed. Reverse- Recommends, Suggests, and Enhances don't need to be tested, and are listed for completeness-sake.

python-wtforms-doc
------------------

python-wtforms
--------------
* python-flaskext.wtf
  [X] trusty (Reverse-Depends)
* flask-wtf
  [X] trusty (Reverse-Build-Depends-Indep)
* edubuntu-server-manager
  [ ] trusty (Reverse-Depends)

I tested python-flaskext.wtf and flask-wtf from the backported version here : https://bugs.launchpad.net/trusty-backports/+bug/1587022 .
For edubuntu-server-manager, package doesn't provide a default configuration file. I tried created one, but it seems to need an LDAP domain which I don't have.

python3-wtforms
---------------