Add the format script for composer

[alaminfirdows]

This pull request includes changes to the composer.json file to add a new format script and a minor reordering of class attributes in the AppHeader.vue file to improve readability.

[tnylea]

So, what does the new composer.json addition do? This adds the ability to run composer format. I'm wondering if this is, in fact, necessary. The re-ordering of classes looks good, though.

LMK.

[alaminfirdows]

I mostly use Composer commands, so I thought it might have here.

If others find this useful!

[taylorotwell]

Will let the dust settle a bit before merging this.