Possibility to define options pro repository

It would be nice to have a possibility to define some options (for example required packages) pro repository.

This would simplify mirroring. Also it would speed up some operations - satis will not search for private packages in local repositories and in the other way.

For example this way:

``` JSON
{
"name": "Company",
"homepage": "http://packages.local",
"repositories": [
{
"type": "vcs",
"url": "https://svn.local.local/privaterepository/",
"require-all": true
},
{
"type": "composer",
"url": "https://packagist.org",
"require": {
"zendframework/zendframework" : ">=2.2",
"monolog/monolog": "*"
},
"archive": {
"directory": "dist/ext",
"format": "tar",
"skip-dev": true
}
}
],
"archive": {
"directory": "dist"
},
"require-dependencies": true
}
```

Global options (at root level) would be overriden by options on repository level.