Add support for configuring SSL declaratively

Both Tomcat and Jetty can now be configured to use SSL via the
environment (typically application.properties or application.yml)

Closes #1084

spring-boot-samples/spring-boot-sample-tomcat-ssl/src/main/resources/application.properties

@@ -0,0 +1,4 @@
+server.port = 8443
+server.ssl.key-store = sample.jks
+server.ssl.key-store-password = secret
+server.ssl.key-password = password