[ADD] views reference first part

* basic views & inheritance documentation
* list view documentation
* make @string (on view arch) optional as it's not used anymore, document as
  deprecated
* make ``@on_write`` only allowed if ``@editable`` is set (RNG-wise)
* fix implicit local error in list view
[ADD] list view buttons doc

* need to extract common stuff in "common area" for views?