* Rewrite:
- stopped using deprecated NETWORK_* constants, now Protocol::* should be used
- still left them intact for slow/lazy developers ...
* Removed deprecated NETWORK_* constants as per code reviewer's request.
* Use "LEFT JOIN" to always fetch the item. Needed for update routines.
* New conversion routine that now covers every item
* Post update is now activated
* We now use a hash based upon RIPEMD-320 for content and activity
* The hash doesn't contain the plink anymore
* Legacy item fields are now "null"able
* New hash function for a server unique item hash
* Introduction of the legacy mode (usage of old item fields)
* Code simplification
* We don't need the "uri" fields anymore in item-activity and item-content
* Use the "created" and not the "received" date for the hash
* Avoiding several notices
* Some more warnings removed
* Improved uri-hash / Likes on Diaspora are now getting a creation date
* Corrected the post update version
* Ensure an unique uri-hash
* Don't delete orhaned item data at the moment
* Partly reworked, due to strange behaviour
* Some more parts reworked
* Using the uri currently seems to be more reliable
* Using the uri here as well
* Use the hash values again
* Grouped item fields in different categories
* Notices again
* use the gravity (we always should)
* Added hint for disabled post updates
* Notices ...
* Issue #5337: Personal notes are displayed again
* Use the gravity again
