Added `for` attributes to the labels and corresponding `id` attributes on the input fields.

Swapped the "Max fieldsets" input to be a "number" (HTML5) type.
Prevalue editor CSS tweaks.

General tightening up of the fields/properties.
Fixed the `id`s for the fieldset labels - added the index/position.

Corrected the nested repeater's `id`s with the context of the parent's index/position.
Merge pull request #24 from leekelleher/feature-config-labels

Prevalue Editor labels wired up to fields/inputs