Fix edges not being added in manage_schema

Fixes #788
core: Add David de Boer to contributors file.
core: Oops, forgot to add controller helper module. Sorry about that.
core: allow binary results from validations.
For now map them to lists, later with the binary webmachine replace this with binary only.

(cherry picked from commit 1b18321b38b16a3efffeded792d75cd270cad66a)
core: Add stats about active sessions and page processes per site
doc: add reference to to_integer
media: user more random filenames for previews.
Prevents race conditions between file updates, as was with the old scheme based on a content hash.

(cherry picked from commit 9038bdacea50dff2f1482f441e658afdc85405bf)
media: fix for generating preview filenames if the inserted id is 'insert_rsc'

(cherry picked from commit 660e77b09e82fda489e8640992f4a95e07c22dc0)
core: reworking client/server communication. Now uses ubf-encoded messages with client side delegates.
TODO: documentation and retry of timed out messages from server to client.
Issue #793
core: Refactored z_stats, now uses exometer
Add ack from client to server, retry messages if no ack received.
Add registration of sessions per user, for user level messages.
Add simple queue pruning on timeout.
Add 'dup' flag to messages that are re-send.
Issue #793.
core: fixes for ack messages.
Added support for pruning the session and page transport-message queues.
Issue #793
core: easier API for transporting messages to an user, session or page.
Might need ACL checks for user level messages.
Issue #793
core: ubf serialize the js proplists with binary keys, to prevent unknown atoms on the server.
Cleaned up and commented z_transport.
Issue #793
core: misc fixes and changes for transport.
Issue #793
docs: add documentation for the new transport mechanism.
Issue #793
docs: fix erlang texts in transport doc.
Issue #793
mod_admin: initialize z_editor when switching language tabs. fix #792

Signed-off-by: Marc Worrell <marc@worrell.nl>
core: increase maximum image size for previews

#796
mod_base: Export controller_logon:set_rememberme_cookie/2

It was inconsistent that it was not exported while the other 2
cookie-related functions were.