Add support for blocking contacts and accounts (#260)

* Add blockContact and unblockContact subcommands

* Send blocked status in contacts sync

* Use only one method for blocking and unblocking

* Add blocking/unblocking for groups

* Prevent blocked messages from being printed

* Print blocked property in listContacts and listGroups commands

* Handle BlockedListMessages

* Store blocked state from incoming contact and group sync messages

* Minor changes and corrections

* Add block and unblock commands to man file (and also fix some headings of commands)

src/main/java/org/asamk/Signal.java

@@ -25,6 +25,10 @@ public interface Signal extends DBusInterface {
 
     void setContactName(String number, String name) throws InvalidNumberException;
 
+    void setContactBlocked(String number, boolean blocked) throws InvalidNumberException;
+
+    void setGroupBlocked(byte[] groupId, boolean blocked) throws GroupNotFoundException;
+
     List<byte[]> getGroupIds();
 
     String getGroupName(byte[] groupId);