Omeka Storage Adapter for Google PicasaWeb (simple initial version)

For installation set under section [site] in /application/config/config.ini this option:

    storage.adapter = "Omeka_Storage_Adapter_PicasaWeb"

The table 'omeka_files' expects to be filled with:
- the 'original_filename' should contain an url such as 'https://lh6.googleusercontent.com/-cKuxEVD-SC8/TunFu_at3fI/AAAAAAAA0pM/x-zcRj7yPqE/'
- the 'archive_filename' must be an unique string - ideally something like '100200027.jpg'

No administration interface is implemented yet, import of the links to images into the 'omeka_files' table must be in this moment done by another means (external script for example).

In future it would probably not be hard to make a proper implementation of the Storage with Zend_Gdata_Photos class. Be aware that the limit of 1000 photos per album must be solved then.
An alternative user interface could be done with http://code.google.com/apis/picker/ - but then the integration with Omeka is probably harder then just with the custom Storage class.

This pull request needs a review and proper testing before merging into master.