elapsed_t: use new pickers from the more_pickers module, add seconds display settings

[paul-arg]

[paul-arg]

What's new in this MR:

• added a settings for when the seconds should be displayed:
• now using the pickers from my more_pickers library to select the target date and time:

[bobrippling]

Thanks! It looks like howManyDaysInMonth is unused, are you ok to delete it?

[thyttan]

Hi @paul-arg! I saw your active again - what do you think of @bobrippling's question above?

[paul-arg]

Hi @thyttan , sorry I completely forgot about this! I have removed the unused function in my latest commit. Thanks!

[thyttan]

OK - thanks!