Test toolkits rebase

This is a rebase of #1422 on the 1.3.x branch. 

Running:
```python
python tests.py
``` 
Will run these tests in addition to the standard mpl ones. 

To run the tests from within python do:

```python
mpl_toolkits.test()
```

This only runs the toolkits tests. 

Note that I had to change the baseline images. Some of these are simply due to changes in freetype but some also seems to involve changes to axis lims. Not sure why.

All tests are at this stage for axisgrid1 and borrowed from the mpl documentation.