XD-783: Alternate Module Registry Layout

Leverages Boot's Archive support (allowing module authoring using Boot related tools, eg maven/gradle plugins)

Supports the following layout:

```
<metaroot>/
           some.jar/
                    lib/
                       3rd-party.jar
                    spring-xd/
                             <type>/<name>.xml
                             <type>/<name>.xml
           somedir/
                    lib/
                       3rd-party.jar
                    spring-xd/
                             <type>/<name>.xml
                             <type>/<name>.xml
```


The "spring-xd" part is here to prevent accidental detection of any xml file as a module (arguably, could be lifted)

The lib/ prefix for extra classpath is compatible with the boot way. Nevertheless, by adding an extra parameter for resolution (eg derived from module options), we're this close to XD-1032:
```
<metaroot>/
           hadoop-modules.jar/
                             lib-hadoop-1.0/
                                       <lots-of-jars>
                             lib-hadoop-2.0/
                                       <lots-of-jars-too>
                             spring-xd/sink/hdfs.xml
```