Tutorial and changes in functions to export to file

[cronosnull]

First part of a small tutorial of data cube use, changes on analytics_utils to export to files

[woodcockr]

Pull request looks good. Could you please do these changes on the develop branch and resubmit?
The master branch is being used for releases only.

The multilingual nature of the project is a new one for us. We suggest the following might be a useful standardization:
a) In the python source code we'd like standardise on English only. No issue with this pull request because there are no new comments in the python source code
b) for the ipython notebooks we'd like to standarise on having two separate versions, one in English and one in Spanish rather than all in one as suggested.

Thanks for the contribution, we hope the changes suggested are easy enough to do. Look forward to seeing more of your work.

[cronosnull]

I'll make the proposed changes and resubmit to development branch.