Add sds submodule

Linked to my own fork because of https://github.com/antirez/sds/pull/18.
Load stops from persistant memory
Allow configuration

The settings aren't transmitted to Pebble yet.
Refactor stops handling in a separate file
Implement transfering stops to Pebble
Shorten "Karlsruhe" in the stop list
Use Base64 encoding to fix äöüß issues
Implement stops reloading without restarting
Fix crash when closing departures window too early

Not sure why this didn't happen before...
Fix default stops not showing with 0 favorites
Change default stations

These might be more useful to the general public.
Fix null pointer when switching stops too fast
Cancel sending messages when getting a new request