Configurable rotate cursor on transformer

[iloabn]

Add tests for and ability to change rotate anchor cursor for transformer.
One test for verifying that the default cursor works, another for verifying that it works to change cursor.

Not really sure about the addition of the rotateCursor to the method getCursor.

Previously it looked like this:

function getCursor(anchorName, rad) {
if (anchorName === 'rotater') {
  return 'crosshair';
}

and now it looks like this

function getCursor(anchorName, rad, rotateCursor) {
if (anchorName === 'rotater') {
  return rotateCursor;
}

• I'm unsure if there's a better way or if this is the way to go?
• Also a little new to writing these types of canvas tests, used another test as a starting point and don't think there's any redundant code in there, but would love suggestions or pointers on how it could be improved.
• Finally, should I add a rotateAnchorCursorChange to the ATTR_CHANGE_LIST as well?

Closes #1590