Add new UI method to switch between required metadata and optional

metadata without incurring in metadata value loss.
Add modifying relationship of document type and metadata type
from the document type and from the metadata type views.
Closes GitLab issues #337 #373.

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

docs/releases/2.5.rst

@@ -44,7 +44,14 @@ Other Changes
   its own separate $HOME directory. Additionally give every libreoffice
   its own UserInstallation file in the $HOME directory. Works around
   Libre Office issue: https://bugs.documentfoundation.org/show_bug.cgi?id=37531
-  Solves or affects GitLab issues #393 #258 #198 #175 
+  Solves or affects GitLab issues #393 #258 #198 #175
+- Document type-metadata type relationship. Add new UI method to switch between
+  required metadata and optional metadata for a document type. This new
+  method does not forces users to remove a metadata type before making the
+  switch and thus avoid deletion of existing metadata entries. GitLab issue #337.
+- It is now possible to change the relationship between metadata types and
+  document types from either the metadata type list or document type list.
+  GitLab issue #373.
 
 
 Removals
@@ -103,5 +110,7 @@ Bugs fixed or issues closed
 * `GitHub issue #255 <https://github.com/mayan-edms/mayan-edms/issues/255>`_ Uploading a local file via api
 * `GitLab issue #215 <https://gitlab.com/mayan-edms/mayan-edms/issues/215>`_ Download text contents
 * `GitLab issue #286 <https://gitlab.com/mayan-edms/mayan-edms/issues/286>`_ User configurable mailer
+* `GitLab issue #337 <https://gitlab.com/mayan-edms/mayan-edms/issues/337>`_ Better way to switch Optional to Required Metadata
+* `GitLab issue #373 <https://gitlab.com/mayan-edms/mayan-edms/issues/373>`_ (feature request) Allow selecting document types for metadata
 
 .. _PyPI: https://pypi.python.org/pypi/mayan-edms/