Mod utils

The show_map function has the "log" keyword argument now to show the log of the maps. For the steeply falling spectra that we are dealing with this might be necessary.
Also, the default label for the zenith axis is fancier now:
![index](https://cloud.githubusercontent.com/assets/7225179/3749892/601ea610-17f0-11e4-8430-08c19e76fead.png)

Matplotlib will automatically set vmin = min(cmap), vmax = max(cmap) like in the example plot above. These lines are there to make the z axis range either symmetric about or start at (if there are only +ive values) zero by default. For a logarithmic scale this behavior doesn't make sense.