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
I still think it's better to list the exceptions explicitly because by using a superclass, you might accidentally catch some exceptions you didn't mean to (someone might add code to this method in the future that throws a new exception).

In Java 7, you can catch multiple exceptions very concisely using `|`:
```
catch (IOException|ProjectManagerException e) {
  ...
}
```
Source: http://docs.oracle.com/javase/7/docs/technotes/guides/language/catch-multiple.html