Use clientlogin API module

This is the first step to allowing 2 factor authentication #328.
This uses the new API module clientlogin instead of the login module.

We still report the same set of errors in a 'nice' way with real
error messages, how ever there are lots more that can probably be
handled, for example #507.

app/src/main/java/fr/free/nrw/commons/MWApi.java

@@ -0,0 +1,58 @@
+package fr.free.nrw.commons;
+
+import java.io.IOException;
+
+import org.apache.http.impl.client.AbstractHttpClient;
+import org.mediawiki.api.ApiResult;
+
+/**
+ * @author Addshore
+ */
+public class MWApi extends org.mediawiki.api.MWApi {
+
+    public MWApi(String apiURL, AbstractHttpClient client) {
+        super(apiURL, client);
+    }
+
+    /**
+     * @param username String
+     * @param password String
+     * @return String On success: "PASS"
+     *                   failure: A failure message code (deifned by mediawiki)
+     *                   misc:    genericerror-UI, genericerror-REDIRECT, genericerror-RESTART
+     * @throws IOException On api request IO issue
+     */
+    public String login(String username, String password) throws IOException {
+
+        /** Request a login token to be used later to log in. */
+        ApiResult tokenData = this.action("query")
+                .param("action", "query")
+                .param("meta", "tokens")
+                .param("type", "login")
+                .post();
+        String token = tokenData.getString("/api/query/tokens/@logintoken");
+
+        /** Actually log in. */
+        ApiResult loginData = this.action("clientlogin")
+                .param("rememberMe", "1")
+                .param("username", username)
+                .param("password", password)
+                .param("logintoken", token)
+                .param("loginreturnurl", "http://example.com/")//TODO return to url?
+                .post();
+        String status = loginData.getString("/api/clientlogin/@status");
+
+        if (status.equals("PASS")) {
+            this.isLoggedIn = true;
+            return status;
+
+        } else if (status.equals("FAIL")) {
+            return loginData.getString("/api/clientlogin/@messagecode");
+        }
+
+        // UI, REDIRECT, RESTART
+        return "genericerror-" + status;
+    }
+
+
+}