Configurable ish Viewport Range

• ADD: Configure ish viewport S, M, L range | #46 #54

Now users may specify an optional configuration entry within the configuration.

• patternlab-config.json (Node)
• config.yml (PHP)

  "ishViewportRange": {
    "s": [240, 500],
    "m": [768, 768],
    "l": [800, 2600]
  },

The first entry in ishViewportRange.s is the ishViewportMinimum, which can now be deleted from your config
The second entry in ishViewportRange.l is the ishViewportMaximum, which can now be deleted from your config

If this new configuration entry is not found, behavior reverts to the hard-coded values.