refine current date/time hotkey handling

Nearing the "do what I mean" principle..

* key date on time cell  =>  current date + time of cell  =>  date+time formatted cell
  * unless time cell was empty or 00:00 time  =>  current date  =>  date formatted cell
* key date on date+time cell  =>  current date + 00:00 time  =>  date+time formatted cell
  * unless date was current date  =>  current date  =>  date formatted cell
* key date on other cell  =>  current date  =>  date formatted cell
* key time on date cell  =>  date of cell + current time  =>  date+time formatted cell
  * unless date cell was empty  =>  current time  =>  time formatted cell
* key time on date+time cell  =>  current time  =>  time formatted cell
  * unless cell was empty  =>  current date+time  =>  date+time formatted cell
* key time on other cell  =>  current time  =>  time formatted cell

Change-Id: I5025e0d0ea9ac83d1b9e0b130262df6db4693a56
update input bar with new value

If setting the number format isn't called we need to explicitly update
the input bar.

Change-Id: I60c4808ce86eb659d3faf92d368c5118ee9673b2