🚚(backend) rename Impress to Meet

I have updated all references of "Impress" to "Meet".
Migrations were manually updated and not regenerated. Never-mind,
they all will be squashed before the first release.

I have also searched for reference to "Magnify", and replaced them
by "Meet".

While updating the backend sources, I have also fixed other parts of
the project, namely:
- Compose file
- Github documentation and CI
- Makefile commands

src/backend/locale/en_US/LC_MESSAGES/django.po

@@ -199,10 +199,10 @@ msgstr ""
 msgid "Either user or team must be set, not both."
 msgstr ""
 
-#: impress/settings.py:134
+#: meet/settings.py:134
 msgid "English"
 msgstr ""
 
-#: impress/settings.py:135
+#: meet/settings.py:135
 msgid "French"
 msgstr ""

src/backend/locale/fr_FR/LC_MESSAGES/django.po

@@ -199,10 +199,10 @@ msgstr ""
 msgid "Either user or team must be set, not both."
 msgstr ""
 
-#: impress/settings.py:134
+#: meet/settings.py:134
 msgid "English"
 msgstr ""
 
-#: impress/settings.py:135
+#: meet/settings.py:135
 msgid "French"
 msgstr ""