Experimental - Projectlayer

Hi Kliment,  

As requested a pull request with the latest projectlayer work I have done.

Most changes are solely in projectlayer.py, but the svg library changed from printrun/svg to printrun/cairosvg

There are also 5 commits which you may wish to cherrypick out (if that's possible) because I changed some of the core functionality so that temperatures are integers, and I added some more logging because I was getting random serial exceptions, these are listed below.

Thinking about it it might be simpler to manually copy in the latest projectlayer.py and the cairosvg library, because when I attempted to merge in your branch there are a lot of formatting differences.  I don't know what formatter you use, but my PyDev couldn't match it no matter what settings I tried.  Your call of course.

Let me know if there's any troubles.  Oh, and I wrote up most of the functionality on a blog page here:  http://garyhodgson.com/reprap/projectlayer/

Cheers,
Gary

more info for serial exceptions	 6afe458
temperatures as integers	 73241a3
distinguish serial exception@	 296b001
Merge branch 'experimental-merge' of /mnt/fileshare/git/Printrun into experimental-merge 25bc48d
fixed temp as ints bug	 2196428