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 cef
grunt cef-clean
grunt cef-download
grunt cef-extract
grunt cef-symlinks
grunt node
grunt node-clean
grunt node-win32
grunt node-darwin
grunt create-project
```