datetime: Remove unused property setters/getters
datetime: Fix typo in function name
datetime: Clean up indentation of the ui file

This was done with xmllint --format; no functional changes.
datetime: Fix the width of hour and minute spinbuttons

Since gtk+ commit cf4a41a856b56bcab6edaaf0e0a4f17ed5853525, the hour and
minute spin buttons in the datetime dialog grew too wide. gtk+ now
computes separate natural and minumum width; unfortunately the natural
width is too wide for us.

Force the spin buttons to have max width of 2 characters to fix this.
Updated Ukrainian translation