Use webjars for static resources in sample apps

samples/httpsession-xml/build.gradle

@@ -5,6 +5,7 @@ apply from: SAMPLE_GRADLE
 dependencies {
 	compile project(':spring-session-data-redis'),
 			"org.springframework:spring-web:$springVersion",
+			"org.webjars:bootstrap:$bootstrapVersion",
 			jstlDependencies
 
 	providedCompile "javax.servlet:javax.servlet-api:$servletApiVersion"
@@ -12,4 +13,4 @@ dependencies {
 	testCompile "junit:junit:$junitVersion"
 
 	integrationTestCompile gebDependencies
-}
+}