ENH: Axis labeling should be more flexible

At present, if you were to specify something like:

```python

yt.load_uniform_grid(data, geometry = ( "geographic", ("latitude", "longitude", "pressure")))

```

yt would get confused, as the axes do not match those that it expects.  I think we should be more flexible in allowing for these aliases, specifically in coordinate systems where we are able to infer what they are.
