WForms2 compatibility – resumed

The last pull request did not include the required changes to the travis.txt requirements file – it therefore was still using WTForms 1.

Then the meta is needed to pass the tests.

I brought this mayhem over me all by myself, please make double sure this works now.
What about calling it: `.travis-requirements-minimal.txt` and `.travis-requirements-released.txt`:

**minimal**
```text
Flask==0.7
wtforms<2.0
Flask-SQLAlchemy==0.15
peewee==?
wtf-peewee==?
```

**released**
```text
Flask
wtforms>=2.0
Flask-SQLAlchemy
peewee
wtf-peewee
```

and maybe we can even test latest **development** versions in the future:
```
-e git+git://github.com/mitsuhiko/flask.git#egg=Flask
...
-e git+git://github.com/mitsuhiko/flask-sqlalchemy.git#egg=Flask-SQLAlchemy
...
```

Thank you very much for your effort.