implement advanced time and date

[liamzebedee]

• implement UI for datetime
• disambiguate between times and datetimes in the DB and Metric view

particularly so I can do stuff like - hours slept (stored as a datetime), represented as {int}.{quarter} (1 ¼ hours), days worked (4.5 days).

something Excel is TERRIBLE at

[liamzebedee]

also add the formatting "X hours" etc.

[liamzebedee]

use cases:

• I want to track how many hours of sleep
• hours and minutes of exercise
• last date when I didn't push myself hard enough

This involves the Date object which stores year to milliseconds. Need a flag which identifies whether it should be represented as either a time (days/hours/minutes) or a date (12/2/15 such and such time).