Bad default XY bookmarks

[ericweiner]

(v 2.1.0 but think this has always been true...)

In the settings/current JSON, the XY bookmarks are:

"bookmark": {
"x": 50000.0,
"y": 75000.0,
"z": 4950.0

These are in mm, not microns, so these numbers are not good, you just go off the edge of the plate.

We should probably just set it to A1 on a 96well plate, as the initial default. x = 14.38, y= 11.24 mm
I think the Z is probably ok...