Output "SharedContacts" field from a SignalDataMessage (#529)

* Initial version of SharedContacts from data message. Need to change location of avatar downloaded and fix plain text mode

* Made empty strings for json null and fixed plaintext output

* Removed old comments, simplified if-statement and added a 'leadingSpaces' field to the print attachments/mentions functions

* Added AsamK's changes

src/main/java/org/asamk/signal/json/JsonSharedContact.java

@@ -0,0 +1,75 @@
+package org.asamk.signal.json;
+
+import com.fasterxml.jackson.annotation.JsonInclude;
+import com.fasterxml.jackson.annotation.JsonProperty;
+
+import org.whispersystems.signalservice.api.messages.shared.SharedContact;
+
+import java.util.List;
+import java.util.stream.Collectors;
+
+public class JsonSharedContact {
+
+    @JsonProperty
+    final JsonContactName name;
+
+    @JsonProperty
+    final JsonContactAvatar avatar;
+
+    @JsonProperty
+    @JsonInclude(JsonInclude.Include.NON_NULL)
+    final List<JsonContactPhone> phone;
+
+    @JsonProperty
+    @JsonInclude(JsonInclude.Include.NON_NULL)
+    final List<JsonContactEmail> email;
+
+    @JsonProperty
+    @JsonInclude(JsonInclude.Include.NON_NULL)
+    final List<JsonContactAddress> address;
+
+    @JsonProperty
+    final String organization;
+
+
+    public JsonSharedContact(SharedContact contact) {
+        name = new JsonContactName(contact.getName());
+        if (contact.getAvatar().isPresent()) {
+            avatar = new JsonContactAvatar(contact.getAvatar().get());
+        } else {
+            avatar = null;
+        }
+
+        if (contact.getPhone().isPresent()) {
+            phone = contact.getPhone()
+                    .get()
+                    .stream()
+                    .map(JsonContactPhone::new)
+                    .collect(Collectors.toList());
+        } else {
+            phone = null;
+        }
+
+        if (contact.getEmail().isPresent()) {
+            email = contact.getEmail()
+                    .get()
+                    .stream()
+                    .map(JsonContactEmail::new)
+                    .collect(Collectors.toList());
+        } else {
+            email = null;
+        }
+
+        if (contact.getAddress().isPresent()) {
+            address = contact.getAddress()
+                    .get()
+                    .stream()
+                    .map(JsonContactAddress::new)
+                    .collect(Collectors.toList());
+        } else {
+            address = null;
+        }
+
+        organization = contact.getOrganization().orNull();
+    }
+}