Download a single artifact file from within the job's artifacts archive.
Only a single file is going to be extracted from the archive and streamed to a client.

1) Added a method to get languages used in a project.
2) Added LicensesApi & MarkdownApi classes and methods

Added getProject() methods which return a single project with statistics and methods for retrieving project archives with a specified format. (#200)

* add project statistics information to Project model

* fix update user bug.
`skip_confirmation` should be `skip_reconfirmation` when updating user.