Fix error where layer power is ignored after first layer.

home only X and Y axes instead of all

Updated GCodes to optimise when it sends PPM and laser power info.
Added a Pronterface option which is enabled by default to allow rasters to be printed with pronterface.
Added M80 command for Tim from LMN

Spent a day stuffing around with the exporter and marlin firmware to figure out why pronterface was throwing checksum errors when
sending lots of G02 and G03 arc vector cuts. It turns out that with too much precision in the cuts marlin's buffer fills up and it's
unable to receive any more serial data. I resolved this by reducing the float point precision down to 3 decimal places and shifting
power and pulse settings to the G00 move command that comes before a set of G01, G02 and G03 commands to limit data that's needed to
be sent over the wire.

I also fixed up the part of the exporter to allow the offset and scaling functions to work. Though I found that looking at the scaling
code it will only scale from the original 0,0 coordinate, it doesn't scale based on a centre point.

I was able to burn vector gcode files with 10000 lines without issue, 30 minute burns with no checksum errors reported by Marlin.

Disabled raster optimisation as it has an alignment bug. Fixed a bug with exporting paths when the origin is the top left

Updated method to determine XY positions of nodes, so query doesnt have to be run for each individual node.

Added capability to export with origin as top left or bottom left- select from exporter plugin menu at the top

Fixed up exporting taking into accoutn stroke, transposing and transforming. This was accomplushed by improving the method of determining the X-Y coordinates of an object that is to be rastered - however it is slower though if you can wait around 2-5 seconds I am sure you willl be fine.