Add support for removing duplicates in concats.js
Add support for removing duplicates in concats.js

Added:
- Argument `concatOptions` to `concatFiles()` function to customize concatenation.
- Option 'removeDuplicates' to `concatOptions` to remove duplicate paths from the array of globbed paths. Defaults to `true`.

The 'removeDuplicates' is useful for customizing the order of files to concatenate, in which globbing will usually sort paths alphabetically.

This option is convenient when the installed glob library does not support removing duplicates on their own (feature supported in 'fast-glob' and 'glob').

Example:

```
/assets/scripts/vendors/a.js
/assets/scripts/vendors/b.js
/assets/scripts/vendors/c.js
/assets/scripts/vendors/d.js
```

```json
"concats": [
    {
        "includes": [
            "{% paths.scripts.src %}/vendors/c.js",
            "{% paths.scripts.src %}/vendors/*.js"
        ],
        "outfile": "{% paths.scripts.dest %}/vendors.js"
    }
]
```

locomotivemtl/locomotive-boilerplate,locomotivemtl/locomotive-boilerplate