timeoverlay: add a datetime time-mode
In this mode, buffer timestamps are displayed as an absolute date since a user-specifiable epoch. The format is also specifiable as a string property, that will be passed to g_date_time_format().
In this mode, buffer timestamps are displayed as an absolute date since a user-specifiable epoch. The format is also specifiable as a string property, that will be passed to g_date_time_format().