component AP: convert AP identity data to XMPP:

metadata are converted to vCard4 (XEP-0292).
Avatar is converted to User Avatar (XEP-0084), it is downloaded, resized, converted and
cached on first request.

If avatar is bigger than 5 Mio, it won't be used.

rel 368

sat/plugins/plugin_comp_ap_gateway/constants.py

@@ -74,3 +74,8 @@ ACTIVITY_TARGET_MANDATORY = ("Add", "Remove")
 ACTIVIY_NO_ACCOUNT_ALLOWED = ("create", "delete")
 # maximum number of parents to retrieve when comments_max_depth option is set
 COMMENTS_MAX_PARENTS = 100
+# maximum size of avatar, in bytes
+MAX_AVATAR_SIZE = 1024 * 1024 * 5
+
+# storage prefixes
+ST_AVATAR = "[avatar]"