Remove animated spinners to lower browser memory usage and increase

responsiveness. Render a document page place holder while the real
document page loads. This change avoids "jumping" effect when
loading many thumbnails. Increase lazy load thresholds. More
thumbnails and document pages will be loaded and visible by
default when a view loads.

Signed-off-by: Roberto Rosario <roberto.rosario.gonzalez@gmail.com>

mayan/apps/common/utils.py

@@ -96,6 +96,13 @@ def get_descriptor(file_input, read=True):
         return file_input
 
 
+def index_or_default(instance, index, default):
+    try:
+        return instance[index]
+    except IndexError:
+        return default
+
+
 def TemporaryFile(*args, **kwargs):
     kwargs.update({'dir': setting_temporary_directory.value})
     return tempfile.TemporaryFile(*args, **kwargs)