Add specific slf4j-api version dependency

When just importing the ftp example as a maven project, I ran into the issue of a slf4j version discrepancy described here:
http://www.slf4j.org/faq.html#IllegalAccessError

This is solved by adding the specific version dependency of `slf4j-api`.

* Add the specific `slf4j-api` dependency to the Gradle script
* Change the dependency scope for `slf4j-` impl to the `runtime`.
* Regenerate POMs

basic/xml/pom.xml

@@ -59,22 +59,22 @@
       <version>4.11</version>
       <scope>test</scope>
     </dependency>
+    <dependency>
+      <groupId>org.springframework.integration</groupId>
+      <artifactId>spring-integration-xml</artifactId>
+      <version>4.2.2.RELEASE</version>
+      <scope>compile</scope>
+    </dependency>
     <dependency>
       <groupId>org.hamcrest</groupId>
       <artifactId>hamcrest-all</artifactId>
       <version>1.3</version>
       <scope>test</scope>
     </dependency>
-    <dependency>
-      <groupId>org.springframework.integration</groupId>
-      <artifactId>spring-integration-xml</artifactId>
-      <version>4.2.0.RELEASE</version>
-      <scope>compile</scope>
-    </dependency>
     <dependency>
       <groupId>org.springframework</groupId>
       <artifactId>spring-test</artifactId>
-      <version>4.2.0.RELEASE</version>
+      <version>4.2.3.RELEASE</version>
       <scope>test</scope>
     </dependency>
     <dependency>