app-container: actool can create app image with fileset dependencies

It is related to #140 

Since app container may contain second optional manifest - `Fileset manifest`, there should be a way to insert it with `actool`.

My change introduces `--fileset-manifest` option that allows user to specify `fileset` with dependencies

Since `appArchiveWriter` now also writes `FilesetManifest`, `fsArchiveWriter` has become redundant, so I removed it.

If  there is no `AppManifest` present it will assume we are adding a file to the fileset.

If `FilesetManifest` is provided along with `AppManifest` it will be written into image "as is".

Example command line:

```
actool build --app-manifest manifest.json --fileset-manifest fileset.json rootfs hello.aci
```