Packaging restx archives

This is a follow up for #62 
I provided a new `app archive` command, allowing to generate a restx archive.

Some insight about the restx archive : the `hello-world` application generated from a `restx app new` will generate something like this :
```
$> tree
.
├── META-INF
│   ├── restx
│   │   └── app
│   │       ├── data
│   │       │   ├── credentials.json
│   │       │   └── users.json
│   │       ├── md.restx.json
│   │       ├── module.ivy
│   │       ├── pom.xml
│   │       └── src
│   │           ├── main
│   │           │   ├── java
│   │           │   │   └── helloworld
│   │           │   │       ├── AppModule.java
│   │           │   │       ├── AppServer.java
│   │           │   │       ├── Roles.java
│   │           │   │       ├── domain
│   │           │   │       │   └── Message.java
│   │           │   │       └── rest
│   │           │   │           └── HelloResource.java
│   │           │   ├── resources
│   │           │   │   └── logback.xml
│   │           │   └── webapp
│   │           │       └── WEB-INF
│   │           │           └── web.xml
│   │           └── test
│   │               ├── java
│   │               │   └── helloworld
│   │               │       └── rest
│   │               │           └── HelloResourceSpecTest.java
│   │               └── resources
│   │                   └── specs
│   │                       └── hello
│   │                           ├── should_admin_say_hello.spec.yaml
│   │                           ├── should_user1_say_hello.spec.yaml
│   │                           └── should_user2_not_say_hello.spec.yaml
│   └── services
│       └── restx.factory.FactoryMachine
├── helloworld
│   ├── AppModule.class
│   ├── AppModuleFactoryMachine$1.class
│   ├── AppModuleFactoryMachine$2.class
│   ├── AppModuleFactoryMachine$3.class
│   ├── AppModuleFactoryMachine$4.class
│   ├── AppModuleFactoryMachine$5.class
│   ├── AppModuleFactoryMachine.class
│   ├── AppServer.class
│   ├── Roles.class
│   ├── domain
│   │   └── Message.class
│   └── rest
│       ├── HelloResource.class
│       ├── HelloResourceFactoryMachine$1.class
│       ├── HelloResourceFactoryMachine.class
│       ├── HelloResourceRouter$1.class
│       ├── HelloResourceRouter.class
│       ├── HelloResourceRouterFactoryMachine$1.class
│       └── HelloResourceRouterFactoryMachine.class
└── logback.xml
```

ATM, I'm packaging sources files into the restx archive (because api doc might rely on it to display source contents)
For the same reason, I package the `src/test/*` file hierarchy.

You can test it easily :
```
restx app new
................
restx app archive /tmp/hello.jar
................
restx app grab file:///tmp/hello.jar + app run
```

FYI, I just created a [`maven-restx-plugin`](https://github.com/restx/restx-maven-plugin) which will re-use the `RestxArchive.pack()` utility method, in order to package a standard restx archive (with `-restx` classifier).

Important note : having the *.class files in the archive is totally useless since the first thing I do in `app grab` is to unzip & chroot to META-INF/restx/app/ directory (then, auto compile does the stuff for us).