Add method to share and un-share project with a group. (#218)

* Add method to share and un-share project with a group.

* Add another method to delete shared group link with ID numbers only.

src/main/java/org/gitlab/api/GitlabAPI.java

@@ -2786,6 +2786,48 @@ public class GitlabAPI {
        return Arrays.asList(response);
    }
 
+    /**
+     * Share a project with a group.
+     *
+     * @param accessLevel The permissions level to grant the group.
+     * @param group       The group to share with.
+     * @param project     The project to be shared.
+     * @param expiration  Share expiration date in ISO 8601 format: 2016-09-26 or {@code null}.
+     * @throws IOException on gitlab api call error
+     */
+    public void shareProjectWithGroup(GitlabAccessLevel accessLevel, String expiration, GitlabGroup group, GitlabProject project) throws IOException {
+        Query query = new Query()
+                .append("group_id", group.getId().toString())
+                .append("group_access", String.valueOf(accessLevel.accessValue))
+                .appendIf("expires_at", expiration);
+
+        String tailUrl = GitlabProject.URL + "/" + project.getId() + "/share" + query.toString();
+        dispatch().to(tailUrl, Void.class);
+    }
+
+    /**
+     * Delete a shared project link within a group.
+     *
+     * @param group   The group.
+     * @param project The project.
+     * @throws IOException on gitlab api call error
+     */
+    public void deleteSharedProjectGroupLink(GitlabGroup group, GitlabProject project) throws IOException {
+        deleteSharedProjectGroupLink(group.getId(), project.getId());
+    }
+
+    /**
+     * Delete a shared project link within a group.
+     *
+     * @param groupId   The group id number.
+     * @param projectId The project id number.
+     * @throws IOException on gitlab api call error
+     */
+    public void deleteSharedProjectGroupLink(int groupId, int projectId) throws IOException {
+        String tailUrl = GitlabProject.URL + "/" + projectId + "/share/" + groupId;
+        retrieve().method("DELETE").to(tailUrl, Void.class);
+    }
+
     /**
      * Set the User-Agent header for the requests.
      *