Apply animal sniffer to entire build

Move animal sniffer configuration out of spring-boot-dependencies to
spring-boot-parent and apply it to all projects.

See gh-716

spring-boot-tools/spring-boot-loader/pom.xml

@@ -20,6 +20,11 @@
 	</properties>
 	<dependencies>
 		<!-- Must never have compile/runtime time dependencies -->
+		<dependency>
+			<groupId>org.springframework</groupId>
+			<artifactId>spring-core</artifactId>
+			<optional>true</optional>
+		</dependency>
 		<dependency>
 			<groupId>org.slf4j</groupId>
 			<artifactId>jcl-over-slf4j</artifactId>