Added support for milliseconds to achievement timestamps

[DoggettCK]

Every profile editor out there that unlocks achievements does so down to a granularity of one second. Someone has written a Greasemonkey/Tampermonkey script that scrapes XBox Live profiles, showing the full timestamps down to the millisecond. On average, you'd unlock 1/1000 achievements right at .000, so if someone has a lot of unlocked achievements with 0ms, it's a good sign they're profile modding.

This patch modifies the datetime editor for the achievement timestamp to use the ISO8601 format, down to the millisecond, and added a few functions to get and set the milliseconds in the timestamps. There are a few places in the new functions where they could be merged with the old ones, like overloading a function and just having the old one call it with 0 milliseconds, or using time_t and uint reference paramters when parsing the time from the 64-bit int instead of having two separate functions, but I didn't want to step on any toes if you'd prefer to keep the old ones around.

[lubo]

You have done an excellent job. Are you going to do the same with avatar awards ?

[DoggettCK]

Sure. I was thinking of that one, as well, since it's the same basic structure.

[DoggettCK]

Added and tested support for Avatar award timestamps as well.

[lubo]

Cool ! Thanks !