(bug 29392) Setting the start or end parameter now works with lists blocks, categorym...

(bug 29392) Setting the start or end parameter now works with lists blocks, categorymembers, deletedrevs, logevents, protectedtitles, usercontributions and watchlist in Postgres.
Since all those used ApiQueryBase::addWhereRange, added ApiQueryBase::addTimestampWhereRange, which does automagic timestamp conversion. Not tested whether this actually fixes problems in Postgres, but at least the API modules are still functional in SQLite