Initial port of download_deps.sh and make_appshell_project.sh

Replaces setup scripts for brackets-shell.

Before:
```
setup.sh # download_deps.sh and make_appshell_project.sh
```

After
```
grunt setup
```

Additional grunt tasks have been broken out for finer grained setup:
```
grunt --help
...
Available tasks
...                                        
            cef  Download and setup CEF                                        
      cef-clean  Removes CEF binaries and linked folders                       
   cef-download  Download CEF, see curl-dir config in Gruntfile.js             
    cef-extract  Extract CEF zip                                               
   cef-symlinks  Create symlinks for CEF                                       
           node  Download Node.js binaries and setup dependencies              
     node-win32  Setup Node.js for Windows                                     
    node-darwin  Setup Node.js for Mac OSX and extract                         
     node-clean  Removes Node.js binaries                                      
 create-project  Create Xcode/VisualStudio project                             
          setup  Alias for "cef", "node", "create-project" tasks.              
...
```