small refactoring on RestxArchiveUnpacker (renamed to RestxArchive) : giving the jar file during instanciation
and using Files.copy() instead of handling streams by hand
Implemented pack() method, allowing to generate a restx jar archive from a working directory
Introduced new `app archive` command, allowing to generate a restx archive
Created RestxBuild.resolveForeignModuleDescriptorsIn() utility method
allowing to retrieve supported foreign (aka non restx) module descriptors
in a given directory
Generating md.restx.json file during `restx app archive` if none is present
Because without these descriptor, the restx archive won't be a real restx archive
(auto download of dependencies won't be possible during `restx app grab + app run`)
Merge pull request #72 from fcamblor/app-archive

Packaging restx archives