mod_carbons: Refactor in new style (mod_mam/csi)

Merge 0.11->trunk

mod_carbons: Fix handling of incoming MUC PMs #1540 27f5db07bec9 fixed this wrong. The code is supposed to check if the stanza is NOT sent to your bare JID. A MUC PM is always sent to your full JID. Hopefully nobody sends MUC invites to full JIDs, because those would be skipped by this as well.

mod_http_files: Avoid using inode in etag, fix #1498

MUC: Adapt rules for what should be stored from mod_mam This is the subset of mod_mam rules I believe makes sense in MUC. Note that mod_muc_mam does not have its own rules, but uses these.

util.sasl.scram: Mention if clients try PLUS without channel binding This isn't normal, but is it invalid? Likely a client bug in any case.

mod_mam: Store only incoming errors Unclear if clients normally ever send error messages, but there may be locally generated bounces sent on behalf of local sessions.

mod_csi_simple: Explicitly mention iq stanzas Should be more obvious that all iq stanzas are considered important. Changes behavior for invalid things in the default namespace.

mod_csi_simple: Clarify what might not be stanzas here

mod_csi_simple: Consider nonzas important This case was previously handled by fall-trough at the end of the function.