Panel / Terms / Add log axis.

In some cases, it may be relevant to provide the capability to have log axis for better readability.

Example:

![image](https://cloud.githubusercontent.com/assets/1701393/4717390/4e86884a-5914-11e4-8d0b-e390dd3212f8.png)

Configuration in the panel options for bar charts:

![image](https://cloud.githubusercontent.com/assets/1701393/4717386/431a0694-5914-11e4-97f9-50c443987102.png)


Bar chart with log axis:

![image](https://cloud.githubusercontent.com/assets/1701393/4717384/34eff164-5914-11e4-8b9d-fca82187bd54.png)



Also fixed some unneeded extra-comma.