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-core/pom.xml

@@ -18,17 +18,9 @@
 			<groupId>io.projectreactor</groupId>
 			<artifactId>reactor-core</artifactId>
 		</dependency>
-		<dependency>
-			<groupId>org.springframework.boot</groupId>
-			<artifactId>spring-boot-starter</artifactId>
-		</dependency>
 		<dependency>
 			<groupId>org.springframework</groupId>
-			<artifactId>spring-context</artifactId>
-		</dependency>
-		<dependency>
-			<groupId>org.springframework.boot</groupId>
-			<artifactId>spring-boot-starter-logging</artifactId>
+			<artifactId>spring-core</artifactId>
 		</dependency>
 		<dependency>
 			<groupId>org.springframework.boot</groupId>