Move gradle includes into gradle/ folder.

Seems to be fairly common layout, and gets them out of the root.

build.gradle

@@ -12,9 +12,9 @@ import java.nio.file.Files;
 import java.nio.file.Paths;
 import static java.nio.file.StandardCopyOption.REPLACE_EXISTING;
 
-apply from: 'clover.gradle'
-apply from: 'local-dependency-change.gradle'
-apply from: 'javadoc.gradle'
+apply from: 'gradle/clover.gradle'
+apply from: 'gradle/local-dependency-change.gradle'
+apply from: 'gradle/javadoc.gradle'
 
 task createWrapper(type: Wrapper) {
     description 'Downloads and installs an up-to-date wrapper for gradle.'