Add decay date to output

[pkienzle]

Give decay date as y-m-d h:m:s in addition to the amount of time to decay below 0.1 nCi.

Assume time off beam gives the time that the sample was removed from the beam (absolute) or the time since the sample was removed from the beam (relative).

E.g.,

    Time to decay below 0.100 nCi is 55.8 yrs (2072-11-13)
    Time to decay below 0.100 nCi is 21.9 days (2018-02-16 07:42)
    Time to decay below 0.100 nCi is 97.2 min (2018-01-15 17:24)

Probably should include the date/time that the sample was removed from the beam as well.

[pkienzle]

First implementaion attempt here:

activation/activation/index.html

Lines 522 to 547 in 45ea300

	/* TODO: show cool-off date.
	The implementation below will confuse users since cool-off date is relative
	to the time off beam rather than the current time. This is okay when the
	"Decay" field is set for an existing sample, but the common case is to
	estimate activation for a sample you are planning to put on the beam not
	one that you have already measured and removed. We could tweak the interface
	so that we only display the cool-off date when decay time is negative or
	decay time is a time stamp, or we could just live with the confusion.
	I'm going to punt on this for now.
	// Add the "cool" date/time as the current time minus off beam time plus decay time.
	var decay_delta = act.decay_time - act.rest[4]; // in hours
	if (decay_delta < 0) {
	// Already past, print nothing.
	} else if (decay_delta < 7*24) {
	// Cool within one week: print date and time
	var decay_date = new Date(Date.now() + 1000*3600*decay_delta); // js timestamp is in ms
	content += ' [date: ' + decay_date.toLocaleString() + ']';
	} else if (decay_delta < HOURS_PER_YEAR*100) {
	// Cool within one century, print date
	decay_delta += 26; // Force anything after 6AM into the next day
	var decay_date = new Date(Date.now() + 1000*3600*decay_delta); // js timestamp is in ms
	content += ' [date: ' + decay_date.toLocaleDateString() + ']';
	} else {
	// More than a century in the future; print nothing.
	}
	*/