Improve compatibility between org-indent-mode and visual-line-mode
* lisp/org-indent.el (org-indent-mode): completely refresh buffer
before starting org-indent-mode. Also set idle timer to refresh only
visible portion of buffer, and refresh the subtree instead of
section when promoting or demoting it.
(org-indent-add-properties): rewrite function to proceed line by
line, as required by `wrap-prefix' specificity.
(org-indent-refresh-section,org-indent-refresh-subtree): refactor.
(org-indent-refresh-view): new function.
(org-indent-refresh-to, org-indent-refresh-section): removed
functions.
* lisp/org.el (org-unfontify-region): do not remove prefix properties
when unfontifying a region.