Some dependency hygiene and update to Boot 1.5.10

The web module doesn't really need to depend on tomcat and all of
the Spring Boot web stack, but users need a way to grab that stuff
quickly if they want it (hence the new starter).

Also removed all spring-boot-starter dependencies from core and
context modules.

spring-cloud-function-context/pom.xml

@@ -15,6 +15,10 @@
 	</parent>
 
 	<dependencies>
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-autoconfigure</artifactId>
+		</dependency>
 		<dependency>
 			<groupId>org.springframework.cloud</groupId>
 			<artifactId>spring-cloud-function-core</artifactId>