Make cleaner setCoords and geometry code

[asturur]

@knagax This PR is mainly about code clean up.
3 methods have been shrunk. Code duplication has been removed and setCoords mad ligther.
Just 4 corners are calculated using the transformation with vpt the other are find "interpolating"
mtr before was a copy of mt , and then made correct in setCornerCoords, now is calculated correct and _setCornerCoords is made simpler.

[asturur]

@kangax Lots of error come out since i moved mtr calculation in setCoords method.
So i have to find out what has screwed up.
Can you get an idea if you like the changes meanwhile?

ok it was related to _calBounds method in group.class.js

Did you ever thought that controls made by circle would made a lot of things easier?
For example find target corner and keeping track of 4 point for each control.

[asturur]

@kangax i'm done. check if you are interested in this.

[kangax]

shouldTransform is better, to indicate that it's boolean

[kangax]

@asturur LGTM. Just please please make sure that everything still works — all the demos, front page of fabricjs.com, grouping, iText, etc.

[asturur]

i have first to clone the repo and install ruby.
no hurry to pull this. i will inform you

[kangax]

Is this good to go?

[kangax]

/cc @asturur

[asturur]

I did not do all that test suite.
I do not have a mirrored copy of fabricjs.com
Trying in next days
(anyway normal testing, playing in kitchsink of course feels fine)

[kangax]

Ok

[asturur]

This code looks to no harm to me, i did check trought all the tests and they look visually the same.,