Use Checkstyle to validate import order

Author: garydgregory

src/conf/checkstyle.xml

@@ -130,6 +130,12 @@
     <!-- <module name="GenericIllegalRegexp"> <property name="format" value="\s+$"/> <property name="message" value="Line has trailing spaces."/> </module> -->
     <module name="TodoComment" />
     <module name="UpperEll" />
+    <module name="ImportOrder">
+      <property name="option" value="top"/>
+      <property name="groups" value="java,javax,org"/>
+      <property name="ordered" value="true"/>
+      <property name="separated" value="true"/>
+    </module>
 
   </module>