[FR] Add -- option to prevent interpretation of filenames with dashes

# Observed behaviour
```
$ touch -- a b -i
$ dragon *
```
The dragon window only show files `a` and `b`, using `-i` as the option (i.e. `--icon-only`).

# Expected behaviour
dragon should interpret `-i` correctly as a file, not as an option. This could be by a `--` option, i.e.
```
$ dragon -- *
```