Stop the pokey container covering the element

* Make the pokey container (.guider_arrow) a rectangle of 42px by 21px
  for up and down pokeys, and 21px by 42px for right and left pokeys, so
  so that it covers as little of the target element as possible
* Reposition the pokey (.guider_arrow_inner) as the size of the
  container has changed
* Move the no-longer-so-magic numbers into variables

Bug: 67179
Change-Id: I1de4f0877fb3cfa1fa7fae799a8771053776f0a4
Merge "Stop the pokey container covering the element"