Add open command, rename get_event to pull
Add open command, rename get_event to pull

* get_event was not really a good name for the command, pull is better
* No need to open a file manually when it's DL from a MISP event:

```
usage: misp open [-h] (-l | -d DELETE | sid)

positional arguments:
  sid                   Sample ID to open (from the list option).

optional arguments:
  -h, --help            show this help message and exit
  -l, --list            List available files
  -d DELETE, --delete DELETE
                        Delete temporary files (use 'all' to remove all the
                        local samples or an Event ID to only remove the
                        associated samples)
```

Beercow/viper,kevthehermit/viper,kevthehermit/viper,S2R2/viper,Beercow/viper,cwtaylor/viper,cwtaylor/viper,MeteorAdminz/viper,Beercow/viper,S2R2/viper,MeteorAdminz/viper