Refactor RRDP URIs storage, implement session ID update.

Refactor RRDP URIs storage, implement session ID update.

+Delete dir daemon: detach thread, renames the directory that's going to be deleted.
+Update logic (structs and relations) to remember RRDP URIs: each TAL thread will hold its own RRDP URIs, and each URI (update notification URI) will have its own visited uris struct; the main thread holds each TALs information, so that it can be accesed during every validation run. This way we know who owns what, and in case of a session ID update it's easier to remove the whole file system directory tree related to an RRDP URI.
+Rename 'visited_uris' of rsync to 'rsync_visited_uris', in validation state struct.
+Assure that update notification files are requested only once per cycle (in case they're found as the prefered access method).
+Implement session ID update, remove all files related to the previous session ID.