Adding get activity and update activity methods

[ldenisey]

garminclient.py - Adding get_activities method to get all the data at once, adding update_activity to modify an activity sample/* - Adding base examples for getting and modifying activities

I needed to clean the activities that I imported from Tomtom sports application. I have refactored and added some methods to query, filter and update activites. I also provided more samples, it might help others.