use a globally unique id when creating new Pidgin::DisplayItem's
Use a globally unique id when creating new `Pidgin::DisplayItem`s as the doc demands and as discussed on [discourse](https://discourse.imfreedom.org/t/how-is-pidgin-id-supposed-to-be-unique/134/2)
Testing Done:
Ran Pidgin and opened a conversation.
Reviewed at https://reviews.imfreedom.org/r/2980/
# SOME DESCRIPTIVE TITLE.
# Copyright (C) YEAR THE PACKAGE'S COPYRIGHT HOLDER
# This file is distributed under the same license as the PACKAGE package.
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# Translators:
# v_ildar <v_ildar@bk.ru>, 2014
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"Project-Id-Version: Pidgin\n"
"Report-Msgid-Bugs-To: \n"
"POT-Creation-Date: 2023-10-31 03:13-0500\n"
"PO-Revision-Date: 2017-09-20 01:06+0000\n"
"Last-Translator: Richard Laager <rlaager@wiktel.com>\n"