Refactor deployer app so that it starts empty

Functions are namespaced under the "app name", e.g.
/sample/uppercase is the "uppercase" function in the "sample" app.

Also added a README to get started quickly.

spring-cloud-function-deployer/README.md

@@ -0,0 +1,56 @@
+Spring Cloud Function Deployer is an app that can deploy functions packaged as jars. Once the app is running it can deploy a basic Spring Cloud Function app from a jar with locally cached dependencies in about 500ms (compared to 1500ms for the same application launched from cold). It can be used in a pool as a "warm" JVM to deploy functions quicker than they could be started from scratch.
+
+The app has a single endpoint called "/admin" that you can use to manage the deployed functions. You GET from it to list the deployed apps, POST to `/{name}` to deploy a named app with a `path` parameter pointing to a jar resource, and then DELETE `/{name}` to remove it. Functions in the apps are exposed as `/{name}/{function}` with the usual conventions for Spring Cloud Function (i.e. the function name is the bean name by default).
+
+== Running the Deployer
+
+Run the main class `ApplicationRunner` in this project (from the command line or in the IDE). E.g.
+
+```
+$ ./mvnw install -DskipTests
+$ cd spring-cloud-function-deployer
+$ ../mvnw spring-boot:run
+```
+
+The app starts empty, so the admin resource shows no deployed apps:
+
+```
+$ curl localhost:8080/admin
+{}
+```
+
+Deploy a sample like this:
+
+```
+$ curl localhost:8080/admin/pojos -d path=maven://com.example:function-sample-pojo:1.0.0.BUILD-SNAPSHOT
+{"id":"81c568e36c7909ec1dd841aa7ee6d3e3"}
+```
+
+(takes about 500ms, once the local Maven cache is warm). Deploy another one:
+
+```
+$ curl localhost:8080/admin/sample -d path=maven://com.example:function-sample:1.0.0.BUILD-SNAPSHOT
+{"id":"cb2fdb3130f6349f143f4686848ea90f"}
+```
+
+Undeploy the first one:
+
+```
+$ curl localhost:8080/admin/pojos -X DELETE
+{"name":"81c568e36c7909ec1dd841aa7ee6d3e3","id":"pojos","path":"maven://com.example:function-sample-pojo:1.0.0.BUILD-SNAPSHOT"}
+```
+
+List the deployed apps:
+
+```
+$ curl localhost:8080/admin
+{"sample":{"name":"sample","id":"cb2fdb3130f6349f143f4686848ea90","path":"maven://com.example:function-sample:1.0.0.BUILD-SNAPSHOT"}}
+```
+
+Send an event to one of the functions:
+
+```
+$ curl -H "Content-Type: text/plain" localhost:8080/sample/uppercase -d foo
+FOO
+```
+