[kronolith] Import / export design

[steve]

I have a design isssue about the import/export feature.
Why would not  we add 2 new drivers (csv file and Palm format)?

Then, we could change the import/export jobs to:
- import from one driver
- export to another driver
In fact, import and export will be the same code (ie. to export, it is 
import from the ical driver and export to the csv driver)

At this point, it would be much easier to add a support to import/export 
from/to another format.

I already took a look of horde/lib/data.php, but I am not sure that 
kronolith/data.php must have in one file all the specific code to handle 
different import/exports.

Last but not least, a such way to do would allow us to add an event 
directly to a yahoo calendar for example, something impossible to do with 
the actual design.

What do you think?

Steve