latex treedoc: convert images to thumbnails for embedding

Images are included by the latex code in full into the rendering,
instead of only the rectangle selected in gramps' media DB. Having lots
of big photos with small faces in my setup, this leads to unreasonably
huge PDF files with unrecognizably small faces in them.

Also, some characters (e.g. comma, spaces) in filepaths might trouble
the latex parser, see 75921ce and 2da93aa -- using thumbnails this
is circumvented.

However, note this makes the resulting .tex file not standalone anymore.

gramps/gen/plug/docgen/treedoc.py

@@ -46,6 +46,7 @@
 from ...constfunc import win
 from ...config import config
 from ...const import GRAMPS_LOCALE as glocale
+from ...utils.thumbnails import get_thumbnail_path
 
 _ = glocale.translation.gettext
 
@@ -589,12 +590,15 @@ def write_node(self, db, level, node_type, person, marriage_flag, option_list=No
                 self.write(level + 1, "comment = {%s},\n" % escape(attr.get_value()))
         for mediaref in person.get_media_list():
             media = db.get_media_from_handle(mediaref.ref)
-            path = media_path_full(db, media.get_path())
-            if os.path.isfile(path):
-                if win():
-                    path = path.replace("\\", "/")
-                self.write(level + 1, "image = {%s},\n" % path)
-                break  # first image only
+            if media.get_mime_type().startswith('image'):
+                path = get_thumbnail_path(
+                    media_path_full(db, media.get_path()),
+                    rectangle=mediaref.get_rectangle())
+                if os.path.isfile(path):
+                    if win():
+                        path = path.replace("\\", "/")
+                    self.write(level+1, "image = {%s},\n" % path)
+                    break # first image only
         self.write(level, "}\n")
 
     def write_event(self, db, level, event):