Optionally announce when entering and leaving blockquotes, lists, and tables

* Announcement is enabled by default, for both navigation and Say All
* Announcement of each object type is independent (e.g. you can enable
  blockquotes, but disable tables and lists)
* Announcement during navigation is independent of announcement during
  Say All (e.g. you can have blockquotes announced during navigation but
  not when using Say All, and tables announced during Say All but not
  during navigation)
* At this time, announcement during Structural Navigation is not impacted
  by these changes. Thus disabling list announcement during navigation
  will not stop Orca from announcing list details when L is used to move
  to the next list. This is intentional.
* In order for this functionality to work, the application or toolkit
  needs to expose the objects to us correctly. For example, LibreOffice
  Writer exposes list items using ROLE_PARAGRAPH; not ROLE_LIST_ITEM. It
  also fails to expose any parent container with ROLE_LIST. This makes it
  difficult to reliably identify the start and end of lists, doubly so
  due to other LibreOffice accessibility bugs. The situation is similar
  for blockquotes. We aren't attempting sad, fragile hacks to work around
  these LibreOffice issues.