Add manifest for `wskdeploy` itself

Since `wskdeploy` can be deployed, we should provide a minimal manifest:

```
package:
name: wskdeploy
version: 0.4.0
description: Utility for deploying and managing Apache OpenWhisk packages and projects
license: Apache-2.0
repositories:
- url: http://github.com/openwhisk/openwhisk-wskdeploy
actions:
exec:
location: actions/exec/exec.zip
runtime: blackbox
```

Notice the `exec` location pointing to a generated zip file, which needs to be checked in so that it can be included by other OpenWhisk projects.

An alternative solution is to have `script` section with commands to generate the zip file.

Ideas?