rename migration
extract update_fulltext
cleanup and sanitize text from rteditor

Following cleanup tasks are performed:
* Strip tags (<div>, ...)
* Strip HTML entities (&uuml;, ...)
* Strip non-readable characters (e.g. carriage return (\r)
break long lines
update content_page scope

content_type=nil also treated as content page
break long lines
move fulltext generation to searchable
add spec for brick after_save hook