[misc] date formatting


For me (and I think most of the world) the mixed endian date format is
very confusing, especially for the first 12 days of the month.  Is it
possible to use ISO 8601 (large to small units) with calcurse?  This is
at least two questions:

 * Can output (calcurse -Q) be presented in YYYY-MM-DD format?
 * Could the appointments in the apt file start with YYYY-MM-DD?

Output should probably follow locale(5), namely $LC_TIME or $LC_ALL.
Saved data should probably follow ISO 8601.