mod_editor_tinymce: improve link function

Add external (generic) link option to menu.
Organize button rows.
When inserting an internal link, use selected text as link label.
core: Refactor authorization in admin controllers. Should fix #782
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