better timing terminology

[Vexcited]

for now we have not really understandable timing, see #6 concerning "Last moment" issue.
also, for posts, we only show seconds late but it's not readable to be honest...

• transform "seconds" to "... ago"
• add day when we go next day above last moment

[Vexcited]

Since f5a448e, on the feed view posts are now labelled with Late of <human format> such as X hours, Y minutes, Z seconds instead of X seconds.