Update the file caching app

- Add view to list available caches.
- Add links to view and purge caches.
- Add permissions.
- Add events.
- Add purge task.
- Remove document image clear link and view.
  This is now handled by the file caching app.

Signed-off-by: Roberto Rosario <roberto.rosario@mayan-edms.com>

mayan/apps/file_caching/icons.py

@@ -0,0 +1,11 @@
+from __future__ import absolute_import, unicode_literals
+
+from mayan.apps.appearance.classes import Icon
+
+icon_file_caching = Icon(
+    driver_name='fontawesome', symbol='warehouse'
+)
+icon_cache_purge = Icon(
+    driver_name='fontawesome-dual', primary_symbol='warehouse',
+    secondary_symbol='check'
+)