Updated tox.ini for local testing.

I updated the tox.ini and tried to get all dependencies and to run as many of the test groups as possible. I also added a description how to install the dependencies for the javascript tests. This might need spelling and wording review.

I get all test groups but rpy2, which has a couple of failing tests. As this test group will be removed soon, this should not be an issue.

```
Tools and libraries available at test time:
   casperjs curses cython jinja2 jsonpointer jsonschema matplotlib mistune numpy pexpect phantomjs pygments pymongo qt requests slimerjs sphinx sqlite3 tornado zmq

Tools and libraries NOT available at test time:
   rpy2
```
Yes, I noticed that creating the virtualenvs takes very long. I think pyside is to blame.
But those are recreated only when the dependencies change - and this shouldn't be too often.
Yes it does increase the test coverage by a very small amount but at least for me it's important to run all the tests.
That's probably not a good default behavior, but I don't think there is a nice solution to handle optional dependencies with tox.