add unicorn_init.sh

`unicorn_init.sh` should be able to read `APP_ROOT/config/unicorn.rb` and
`/etc/unicorn/APP_NAME.conf` and control `unicorn`

I wasn't sure what permissions to set on `unicorn_init.sh`.  I know it will need to be executable.

Still have the minor issue of sending a restart command:

```bash
deployer@testarcsite:~/apps/arcsite/current$ sudo /etc/init.d/unicorn_arcsite restart 
[sudo] password for deployer: 
/home/deployer/apps/arcsite/current: 
Stopping - OK
/etc/init.d/unicorn_arcsite: line 43: kill: (2822) - No such process
/etc/init.d/unicorn_arcsite: line 43: kill: (2822) - No such process
/etc/init.d/unicorn_arcsite: line 43: kill: (2822) - No such process
Starting - OK
```

It seems to not like killing the app and tries to kill the pid multiple times.  Despite these messages, unicorn stops and stats as expected