Add revoke follow feature

- Add new follow revoke module
- Add new hooks: revoke_follow, support_follow, support_revoke_follow
- Add link in contact page action menu

doc/Addons.md

@@ -479,6 +479,22 @@ Hook data:
 - **uid** (input): the user to return the contact data for (can be empty for public contacts).
 - **result** (output): Set by the hook function to indicate a successful detection.
 
+### support_follow
+
+Called to assert whether a connector addon provides follow capabilities.
+
+Hook data:
+- **protocol** (input): shorthand for the protocol. List of values is available in `src/Core/Protocol.php`.
+- **result** (output): should be true if the connector provides follow capabilities, left alone otherwise.
+
+### support_revoke_follow
+
+Called to assert whether a connector addon provides follow revocation capabilities.
+
+Hook data:
+- **protocol** (input): shorthand for the protocol. List of values is available in `src/Core/Protocol.php`.
+- **result** (output): should be true if the connector provides follow revocation capabilities, left alone otherwise.
+
 ### follow
 
 Called before adding a new contact for a user to handle non-native network remote contact (like Twitter).
@@ -497,6 +513,14 @@ Hook data:
 - **two_way** (input): wether to stop sharing with the remote contact as well.
 - **result** (output): wether the unfollowing is successful or not.
 
+### revoke_follow
+
+Called when making a remote contact on a non-native network (like Twitter) unfollow you.
+
+Hook data:
+- **contact** (input): the remote contact (uid = local revoking user id) array.
+- **result** (output): a boolean value indicating wether the operation was successful or not.
+
 ## Complete list of hook callbacks
 
 Here is a complete list of all hook callbacks with file locations (as of 24-Sep-2018). Please see the source for details of any hooks not documented above.
@@ -751,7 +775,11 @@ Here is a complete list of all hook callbacks with file locations (as of 24-Sep-
 
 ### src/Core/Protocol.php
 
+    Hook::callAll('support_follow', $hook_data);
+    Hook::callAll('support_revoke_follow', $hook_data);
     Hook::callAll('unfollow', $hook_data);
+    Kook::callAll('revoke_follow', $hook_data);
+
 ### src/Core/StorageManager
 
     Hook::callAll('storage_instance', $data);

doc/de/Addons.md

@@ -414,7 +414,12 @@ Eine komplette Liste aller Hook-Callbacks mit den zugehörigen Dateien (am 01-Ap
     Hook::callAll('logged_in', $a->user);
 
 ### src/Core/Protocol.php
+
+    Hook::callAll('support_follow', $hook_data);
+    Hook::callAll('support_revoke_follow', $hook_data);
     Hook::callAll('unfollow', $hook_data);
+    Kook::callAll('revoke_follow', $hook_data);
+
 ### src/Core/StorageManager
 
     Hook::callAll('storage_instance', $data);