Strava download : add error messages
UI Nits: Sidebar WIP

.. some cosmetic and tidy ups for the recent sidebar WIP update
from Damien. Just trying to get clean look before making the icon
bar look more like the one in XCode and make the icons use the
Cocoa "template" look.
Fix SEGV on unsupported device types

.. train tool segvs on device types that were previously
configured but are no longer supported. This fix now silently
ignores any devices that are no longer supported.

Fixes #497.