"verb" for all items, new function for uploading pictures

* The "verb" field wasn't always set when items were created. (It happened with posts from Diaspora, Feeds and Mails) This is now fixed
* There is a new function to upload pictures to the wall. There was only some code in "mod/wall_upload.php" but it wasn't encapsulated enough. This function will be used in connectors when mirroring posts.
* There was a bug in the function "get_attached_data" that is used to return the type of the post. Under certain circumstances the function hasn't detected, that a post was a picture post.
* At the community page we link to the items with the guid. This is now done at the network page as well. This is a preparation for some future changes.