Split all the e2e tests in their own files

Some duplication is avoided, but most importantly: it’s much much cleaner,
easier to find, functions have been cleaned up (functools.partial usages are
now hidden), etc.

tests/end_to_end/scenarios/encoded_channel_join.py

@@ -0,0 +1,11 @@
+from scenarios import *
+
+scenario = (
+    sequences.handshake(),
+    send_stanza("<presence from='{jid_one}/{resource_one}' to='#biboumi\\40louiz.org\\3a80%{irc_server_one}/{nick_one}' />"),
+    sequences.connection("irc.localhost", '{jid_one}/{resource_one}'),
+    expect_stanza("/message/body[text()='Mode #biboumi@louiz.org:80 [+nt] by {irc_host_one}']"),
+    expect_stanza("/presence[@to='{jid_one}/{resource_one}'][@from='#biboumi\\40louiz.org\\3a80%{irc_server_one}/{nick_one}']/muc_user:x/muc_user:item[@affiliation='admin'][@role='moderator']",
+                  "/presence/muc_user:x/muc_user:status[@code='110']"),
+    expect_stanza("/message[@from='#biboumi\\40louiz.org\\3a80%{irc_server_one}'][@type='groupchat']/subject[not(text())]"),
+)