Tentative of streamlining times

Since times were/are a bit inconsistent, this is a first tentative to harmonization.
"Source-side" each time is calculated/provided to the theme in three formats:
* time, that uses relativeTime/standardTime,
* html_time, that uses htmlTime and contains a ```<time>``` tag ready for the js relative time,
* timestamp, that contains the "raw" timestamp coming from the database (probably not so useful, but who knows).

All the places I found with a time now have the triplet, I may have miss some.
In the theme there may be some "absolute times" where there was a relative before, not sure I spot all the changes, a thing to check.

One pending before merge: relativeTime VS standardTime.
At the moment the first simply returns the second, so it could be removed, or we could keep it just in case we change our minds "later", and use standard time in all the other places. Opinions?