Support the ability to download project zip file #373

* A new button is displayed on the project page to download the project zip file
* One can use curl to download the project zip file
curl -O -J -k --get --data "session.id=<session id>&project=<project nane>&download=true" http://<websever host>:<port>/manager
May be on a tangential line but can we give user an option to switch zip file version for a project ? may be something like undo ?