Obscure date/time for private/obscured obs the user does not have access to

[tiwane]

Simliar to the way we do it on the web: if the user does not have access to an obscured/private observation via user-to-user or project trust, the user should only see the month and year of the observation on the observation detail screen. Date/time of IDs and comments should also only show month and year.

Relative times should also only show month and year, this should cover other users' lists of observations, eg when I tap on someone's username and I'm taken to the screen that shows their list of observations.