Watch folders: Add support for subfolders

Add support for subfolder scanning to watch folders. Closes
GitLab issue #498 and #563.

This commit adds a new field to watch folders called
"include_subdirectories".

The directory walk was also updated to use pathlib2.

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

docs/releases/3.2.rst

@@ -0,0 +1,87 @@
+Version 3.2
+===========
+
+Released: XX XX, 2019
+
+
+Changes
+-------
+
+
+Other changes
+^^^^^^^^^^^^^
+
+* Split source models into different modules.
+
+Removals
+--------
+
+* None
+
+
+Upgrading from a previous version
+---------------------------------
+
+If installed via Python's PIP
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Remove deprecated requirements::
+
+    $ curl https://gitlab.com/mayan-edms/mayan-edms/raw/master/removals.txt | pip uninstall -r /dev/stdin
+
+Type in the console::
+
+    $ pip install mayan-edms==3.2
+
+the requirements will also be updated automatically.
+
+
+Using Git
+^^^^^^^^^
+
+If you installed Mayan EDMS by cloning the Git repository issue the commands::
+
+    $ git reset --hard HEAD
+    $ git pull
+
+otherwise download the compressed archived and uncompress it overriding the
+existing installation.
+
+Remove deprecated requirements::
+
+    $ pip uninstall -y -r removals.txt
+
+Next upgrade/add the new requirements::
+
+    $ pip install --upgrade -r requirements.txt
+
+
+Common steps
+^^^^^^^^^^^^
+
+Perform these steps after updating the code from either step above.
+
+Migrate existing database schema with::
+
+    $ mayan-edms.py performupgrade
+
+Add new static media::
+
+    $ mayan-edms.py collectstatic --noinput
+
+The upgrade procedure is now complete.
+
+
+Backward incompatible changes
+-----------------------------
+
+* None
+
+
+Bugs fixed or issues closed
+---------------------------
+
+* :gitlab-issue:`498` Can't scan subdirectories
+* :gitlab-issue:`563` Recursive Watch Folder
+
+.. _PyPI: https://pypi.python.org/pypi/mayan-edms/