feat(Groupware/Contacts): add contacts multiactions and contact merging

Signed-off-by: Grigory Vodyanov <scratchx@gmx.com>

Author: GVodyanov

user_manual/groupware/contacts.rst

@@ -110,6 +110,31 @@ click on the contacts picture for the following options to appear:
 
 .. figure:: ../images/contact_picture_options.png
 
+Managing multiple Contacts at a time
+------------------------------------
+
+The Contacts app enables you to select multiple contacts at a time and to perform batch actions on them. To select a contact in multiselection mode, click on their profile picture, or shift click them, in the contacts list.
+
+This will bring up a menu at the top of the contacts list with various actions you can perform on the selected contacts:
+
+.. figure:: images/contact_multiselect.png
+    :alt: Contact multiselect actions
+
+The cross icon will exit multiselection mode, deselecting all contacts, while the trash bin icon will delete the selected contacts.
+
+.. note:: You might not be able to modify or delete certain contacts, for example if they are in a read-only address book. In that case, relevant actions will be disabled.
+
+Merging duplicate Contacts
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The merging icon in the multiselect menu will open a dialog that helps you merge duplicate contacts. The merging dialog will show the details of both contacts side by side, and you can choose which details to keep in the merged contact.
+
+Radio (circular) buttons let you choose only one of the two versions (like the name of the contact, which can only have one value), meanwhile checkboxes (square buttons) allow you to keep both values if desired (like phone numbers or email addresses, where a contact can have multiple values).
+
+If the contacts are part of groups, by default the merged contact will be part of all groups that either of the two contacts was part of. You can uncheck groups while merging if you don't want the merged contact to be part of them.
+
+.. note:: Currently you are only able to merge two contacts at a time, and you are naturally only able to merge contacts that can be modified by you. If the merging action is disabled, check that you selected contacts that match those conditions.
+
 Organize your Contacts with Contact Groups
 ------------------------------------------