Old GarminConnect GAUTH no longer working - deprecated

[AngelaKru]

So Garmin have finally deprecated their old legacy authentication and APIs, so this wonderful script stopped working a few days ago.
I've been digging and testing this and that, and finally found the correct URLs for the 'modern' authentication and activities download, and was able to compare the old JSON results to the new.
I've created a PR with these changes - it work for me, using Python 2.7 and Mechanize package (when I have time I want to test alternatives to allow me to run this on Python 3.x...)

[magsol]

A breaking issue, a fix, and a PR!

A fix, even for Python 2.7.x, is absolutely happily received. Thank you!