Revert "/journey/edit: datetime inputs"

This reverts commit 02a6b907.

DateTime inputs on the web are absolutely horribly broken as soon es they use
sub-minute accuracy (i.e., seconds). Switch journey edits back to %d.%m.%Y
%H:%M(:%S) to restore proper editing support. /journey/add and /checkin/add
retain their datetime pickers and will not support sub-minute accuracy.

Closes #272