Add support for loconfig.local.json

If a 'loconfig.local.json' file is present (ignored by git), its settings will be merged with those in 'loconfig.json'. Useful for customizing localhost development (see example below).

Added:
- Utility 'config.js' to prepare build settings.
- Function 'merge()' for recursively merging objects and concatenating arrays.

Example:

```json
{
    "paths": {
        "url": "yourlocal.dev"
    },
    "server": {
        "open": true,
        "https": {
            "key": "~/.config/valet/Certificates/{% paths.url %}.key",
            "cert": "~/.config/valet/Certificates/{% paths.url %}.crt"
        }
    }
}
```

.gitignore

@@ -1,3 +1,4 @@
 node_modules
 .DS_Store
 Thumbs.db
+loconfig.*.json