Release 4.10

This is a tracking issue for release 4.10.

**Please keep feature requests in their own issues**

If you want to make a comment on a particular change, please make the comment in the "Files changed" tab so comments are not lost during a rebase (they may occur on patches to the previous release).

List of changes for release:
- [x] Add support for array of view directories #2320
- [x] Use `content-disposition` module for `res.attachment` for better standards

**Testing this release**

If you want to try out this release, you can install it with the following command:
```bash
$ npm install strongloop/express#4.10
```

Owners/collaborators: please do not merge this PR :)