* src/widgets/modest-gtkhtml-msg-view.c:

* src/widgets/modest-gtkhtml-msg-view.c:
        * Add implementation of external images fetching. We show a
          button for letting user accept external images when they're
          available.
        * Rework all the external images fetching code to use the
          new tinymail stream cache.
* src/widgets/modest-gtkhtml-mime-part-view.c:
        * Fix some issues in the way we created the streams to avoid
          some crashes.
        * Now images retrieval should happen in msg view window layer,
          not on msg or mime part view.
        * Implement new ModestMimePartView methods to know if we
          can view images. Also use the TnyMsg information to show if
          we can fetch external images.
* src/widgets/modest-msg-view.c:
        * New signal fetch-image to let upper layers handle retrieving
          images from external sources.
        * New methods set view images and get view images to set if
          the user can view external images.
* src/widgets/modest-mime-part-view.c:
        * New methods to get/set view images state, and to know if a
          message has external images.
* src/widgets/modest-tny-stream-gtkthml.[ch]:
        * Keep a reference to the GtkHTML to keep it alive while stream
          is alive.
* src/maemo/modest-msg-view-window.c:
        * Handle new ModestMsgView signal "fetch-image", using the new
          stream cache. Now all the image retrieval happens here, using
          that cache as backstore.
* src/maemo/modest-account-settings-dialog.c:
        * Fix leaks in sizegroups.
* src/modest-utils.[ch]:
        * Added a new method to get the cache id we'll use to store the
          images in image cache.
* src/modest-runtime.[ch]:
        * Added method to retrieve the images cache singleton.
* src/modest-singletons.[ch]:
        * Provide a image cache using the TnyFsStreamCache.

pmo-trunk-r4773