Implementation of the documented Services API.

Currently, only a subset of the service API is documented.
https://github.com/gitlabhq/gitlabhq/blob/master/doc/api/services.md

src/main/java/com/messners/gitlab/api/ServicesApi.java

+package com.messners.gitlab.api;
+
+import com.messners.gitlab.api.models.Project;
+
+import javax.ws.rs.core.Form;
+import javax.ws.rs.core.Response;
+
+/**
+ * Access for the services API.
+ * See
+ * <a href="https://github.com/gitlabhq/gitlabhq/blob/master/doc/api/services.md">GitLab documentation</a>.
+ * It is quite restricted as you may not retrieve the API but only set or delete.
+ */
+public class ServicesApi extends AbstractApi {
+    public ServicesApi(GitLabApi gitLabApi) {
+        super(gitLabApi);
+    }
+
+    /**
+     * Activates the gitlab-ci service.
+     *
+     * PUT /projects/:id/services/gitlab-ci
+     * @param projectId id of the project
+     * @param token for authentication
+     * @param projectCIUrl URL of the GitLab-CI project
+     */
+    public void setGitLabCI(Integer projectId, String token, String projectCIUrl) throws GitLabApiException {
+        final Form formData = new Form();
+        formData.param("token", token);
+        formData.param("project_url", projectCIUrl);
+        put(Response.Status.OK, formData.asMap(), "projects", projectId, "services", "gitlab-ci");
+    }
+
+    /**
+     * Activates the gitlab-ci service.
+     *
+     * PUT /projects/:id/services/gitlab-ci
+     * @param project the project
+     * @param token for authentication
+     * @param projectCIUrl URL of the GitLab-CI project
+     */
+    public void setGitLabCI(Project project, String token, String projectCIUrl) throws GitLabApiException {
+        setGitLabCI(project.getId(), token, projectCIUrl);
+    }
+
+    /**
+     * Deletes the gitlab-ci service.
+     *
+     * DELETE /projects/:id/services/gitlab-ci
+     *
+     * @param projectId id of the project
+     * @throws GitLabApiException
+     */
+    public void deleteGitLabCI(Integer projectId) throws GitLabApiException {
+        delete(Response.Status.OK, null, "projects", projectId, "services", "gitlab-ci");
+    }
+
+    /**
+     * DELETE /projects/:id/services/gitlab-ci
+     * @param project to delete
+     * @throws GitLabApiException
+     */
+    public void deleteGitLabCI(Project project) throws GitLabApiException {
+        deleteGitLabCI(project.getId());
+    }
+
+    /**
+     * Activates HipChat notifications.
+     *
+     * PUT /projects/:id/services/hipchat
+     *
+     * @param projectId id of the project
+     * @param token for authentication
+     * @param room HipChat Room
+     * @param server HipChat Server URL
+     *
+     * @throws GitLabApiException
+     */
+    public void setHipChat(Integer projectId, String token, String room, String server) throws GitLabApiException {
+        final Form formData = new Form();
+        formData.param("token", token);
+        formData.param("room", room);
+        formData.param("server", server);
+        put(Response.Status.OK, formData.asMap(), "projects", projectId, "services", "hipchat");
+    }
+
+    /**
+     * Activates HipChat notifications.
+     *
+     * PUT /projects/:id/services/hipchat
+     *
+     * @param project
+     * @param token
+     * @param room
+     * @param server
+     * @throws GitLabApiException
+     */
+    public void setHipChat(Project project, String token, String room, String server) throws GitLabApiException {
+        setHipChat(project.getId(), token, room, server);
+    }
+
+    /**
+     * Deletes the gitlab-ci service.
+     *
+     * DELETE /projects/:id/services/hipchat
+     *
+     * @param projectId id of the project
+     * @throws GitLabApiException
+     */
+    public void deleteHipChat(Integer projectId) throws GitLabApiException {
+        delete(Response.Status.OK, null, "projects", projectId, "services", "hipchat");
+    }
+
+    /**
+     * Deletes the gitlab-ci service.
+     *
+     * DELETE /projects/:id/services/hipchat
+     *
+     * @param project the project
+     * @throws GitLabApiException
+     */
+    public void deleteHipChat(Project project) throws GitLabApiException {
+        deleteHipChat(project.getId());
+    }
+}