remove fuzzy time from conversation textview and include date in time_stamp
This MR removes "Yesterday"/"X days ago" in front of the timestamp in all conversation textviews (1on1 chat and groupchats).
The config setting "time_stamp" was set to [%x %X] to show the absolute date and time in front of every message.
TODO: I had to manually click "reset" in ACE for the "time_stamp" config setting to get the new default value. Is this automatically done when Gajim will release an update or only on new installs?