Support for embedded Tomcat 8 container parallel to the current Tomcat 7

This patch contains a copy of the spring-boot org.springframework.boot.context.embedded.tomcat package with changed names of the referenced embedded Tomcat API classes which have been moved/renamed between 7.0 and 8.0.0-RC1 releases.
An application which relies upon spring-boot and replaces its transitive dependency to the tomcat 7 (`org.apache.tomcat.embed:tomcat-embed-core:7.0.42`) with a tomcat 8 dependency: `org.apache.tomcat.embed:tomcat-embed-core:8.0.0-RC1` can start embedded tomcat 8 using spring-boot if the following dependency added:
`org.springframework.boot:spring-boot-tomcat8:$springBootVersion`

Changes have been separated to the new projects submodule to workaround the problem of having two versions of tomcat dependencies simultaneously on the classpath at compile time.

This patch is for demo purpose to illustrate changes needed to start the embedded tomcat 8.0.0-RC1 using the spring-boot.