blog (atom feed): fixed atom handling: - atom generation code moved from backend to Libervia - replaced hardcoded urls by urls based on request path - added xmpp: uri as alternate links - feed id was not unique (it was the node), now it is the quoted xmpp uri - atom:updated was using current time which is wrong, now take the more recent item "updated" value - link elements where missing attributes (e.g.: type) - added correct http(s) links for each items - microblog items (without title) now use an abstract of content as title - use 20 as max_items for atom feeds (may change in the future) - removed bad use of encode