Prepare releasenotes for 5.5.3

Author: espenak

not_for_deploy/docs/sysadmin/migrationguides/migrate-from-5.5.2-to-5.5.3.rst

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+=============================
+Migrating from 5.5.2 to 5.5.3
+=============================
+
+Fixes and new features
+######################
+
+- Bugfix: Handle the case where users could upload files to the feedbackfeed, and remove them, and then submit an empty comment.
+
+
+Backup database and files
+#########################
+
+BACKUP. YOUR. DATABASE. AND. FILES.
+
+
+Update devilry to 5.5.3
+#######################
+
+Update the devilry version to ``5.5.3`` as described in :doc:`../update`.

not_for_deploy/docs/user/changelog/5.5.3.rst

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+.. _5.5.3changelog:
+
+############################
+What is new in Devilry 5.5.3
+############################
+
+
+Fixes and new features
+######################
+
+- Bugfix: Handle the case where users could upload files to the feedbackfeed, and remove them, and then submit an empty comment.