OS X: Use LetsMove to simplify installation.

In preparation for shipping OS X builds as ZIP archives, integrate
LetsMove.  When the user launches the app from a location different from
/Applications (e.g.  from the Downloads folder), the app offers to move
itself to the correct place.
OS X: don't leave stray SUFeedURL in user defaults.
Fix randomly broken list sorting.

UErrorCode must be initialized to U_ZERO_ERROR, otherwise collator's
compare() would just return the values are equal (go figure).
Remove the outdated, unused TODO file.