Function insertSorted

insertSorted(parent: HTMLElement, element: HTMLElement): void
Inserts element into parent sorted according to its HTML attribute data-sort.

Assumes:
- Every child of parent and element, has a data-sort attribute. This is the basis for sorting.
- parent starts off empty or pre-sorted.
- Order of parent's children is not changed (ie it always remains sorted)
Parameters
- parent: HTMLElement
  Parent to insert into
- element: HTMLElement
  Element to insert
Returns void