Add Reorder Helper

[dmolsen]

In order to re-order patterns based on documentation (or config?) use the following steps as part of a helper:

• separate the patterns by those with order set and an integer
• sort on order
• merge with sorted by order items first

[sghoweri]

@dmolsen Anything I could do to help out on this (if you had any pointers on where to start chipping away at this)?

I'm in the middle of a Drupal 8 / Pattern Lab 2 for Twig integration project which could really benefit from this (so win win)!