Add dependency management to Gradle build

Otherwise you get old versions of spring-* dependencies. This change
can be reverted when we upgrade to Spring Boot 1.3.

Fixes gh-13

complete/build.gradle

@@ -8,9 +8,12 @@ buildscript {
     }
     dependencies {
         classpath("org.springframework.boot:spring-boot-gradle-plugin:1.2.7.RELEASE")
+        classpath "io.spring.gradle:dependency-management-plugin:0.5.3.RELEASE"
     }
 }
 
+// This wouldn't be needed with Spring Boot 1.3
+apply plugin: 'io.spring.dependency-management'
 apply plugin: 'java'
 apply plugin: 'eclipse'
 apply plugin: 'idea'
@@ -62,6 +65,12 @@ task genJaxb {
 sourceCompatibility = 1.8
 targetCompatibility = 1.8
 
+dependencyManagement {
+     imports {
+          mavenBom 'org.springframework.boot:spring-boot-starter-parent:1.2.7.RELEASE'
+     }
+}
+
 dependencies {
     compile("org.springframework.boot:spring-boot-starter")
     compile("org.springframework.ws:spring-ws-core")