Extensions and restructuring

[ghost]

I've written a few new functions based on your code and, in the process, restructured the code to make it easier to reuse.

You can now reverse the retrieval order, from oldest to newest activity, and get the csv laps file of an acitivity. which allows retrieval of new runs up to a certain given activity. In addition, I have added a function that allows retrieval of new activities up to a certain activity.

I hope you like the restructuring. All the Garmin handling is now in the GarminHandler.py. This is used by gcexport.py, which has the same functionality as before (plus the mentioned extras), but is a lot lighter. The separate handler also allows for reusing the code in different Garmin-related projects where activities need to be retrieved.

Please let me know if you have questions or comments, both on functionality and code-style.