Saving/restoring the user interface state

[azaozz]

Group of functions (php and js) to store the user interface state. Settings are stored in a cookie and saved in the user profile on the next page load (if changed).

When the cookie is deleted or missing or another browser is used, the settings are restored from the last saved cookie.

Currently this is used only for setting the default editor and the state of the second row of buttons in TinyMCE. Potentially can be used to store most (if not all) UI state, like postboxes visibility and position, settings for image size and alignment, etc.

[azaozz]

(In [8784]) Saving/restoring the user interface state, see #7654