code: Add m_edge.id[123].predicate[456] syntax to look up an edge id from a triple

Plus added additional documentation
(cherry picked from commit 5b49bd755eae9d747599e1ab133bfda3d4850fd0)
mod_acl_simple_roles: Fix bug where visible_for would be reset when it was not part of a rsc update call.

When visible_for is not given in the update props, we now leave the
value alone, instead of replacing it with the min_visible_for setting,
which essentially overrode any set value in the database.
(cherry picked from commit afc1725be4f80b2e383982340d66d3c0713beb41)
mod_admin_identity: Add option to send username/password to the user over e-mail

When creating users in the admin, you often want to give them their
user/password immediately afterwards. This "send welcome" checkbox
automates that process by sending the new user an email with the login
credentials.
(cherry picked from commit 5a9f8bf6dd893897a97b648e9ba7bf8ca9568f96)