Issue 85 - Converting user location action links to buttons to fix voice over issues

Changes are:
* Prefer and remove anchors have been changed to buttons, this should fix issues #85, #87 and #90 
* Added an aria-disabled attribute for prefer location button
* Base style for dialog is position: relative (moved from min568) as buttons we displaying above icons.

This change introduces an issue which would need to be fixed before this can be merged:
* The buttons can be tabbed to (shift tab from the confirm button) when they are behind the dialog, there are a number of options to fix which would need to be done before the dialog is displayed and then reset after:
  * Add aria-hidden="true" labels
  * Set tabindex to -1 to remove from tab order
  * Hide with display: none
  * Remove the elements from the DOM

Not entirely sure which solution is best.

Also noticed another existing accessibility issue while working on this, when the dialog has been confirmed or cancelled the focus position is lost and then user is put back to the top of the page, will raise an issue for this.