Possibility to update the packagesMap config

Introduction of an API (`noder.updatePackagesMap`) that allows to update the packagesMap after noder has been already initialized.
I think it is better to write it this way:
```js
var map = this.toFile ? {} : configUtils.getPackagesMap(packaging, this.noderConfig, this.noderContext);
```
I don't understand why it would be needed to have 2 different variables `map` and `outputMap`, but maybe I am missing something, and I suppose there is no need to call `getPackagesMap` when `toFile` is provided.