It turns out elm/uiclock (which was removed in 89675c3219) is actually used,
at least by the datetime legacy widget. Removing this widget broke the
This commit reverts 89675c3219 and fixes the elm/uiclock part names:
- Part names are prefixed with 'elm.'
- efl_ui_clock.c (which is used for both the new efl and the legacy elm widgets) now looks for part names with 'efl.' and 'elm.' prefixes, and without any prefix, for compatibility with older themes.