Simplify bundle vis centering

Simplify bundle vis centering

It turns out that using a polygon centroid isn't quite what our eyes expected, and also caused a bug when elements were away from the center mass of services.  Using the bounding box gives more expected results.

I didn't add a test, because I argued to myself that this was a visual thing, but I'm really lying to myself, and if you want to call me out on it, please feel free to appeal to my better self. :-)

To QA, look at a lot of bundles, like those from "hatch", "jorge", and "gary".  Then also look at the problematic one, http://localhost:8888/sidebar/search/bundle/~makyo/mediawiki-scalable/5/mediawiki-scalable/ .  Compare it with the rendering in trunk (like on comingsoon) to see the difference.

https://code.launchpad.net/~gary/juju-gui/bug1250547/+merge/194932

(do not edit description out of merge proposal)

[gary.poster, 2013-11-12 20:02:38]

Please take a look.

[matthew.scott, 2013-11-12 20:07:01]

LGTM! \o/

[gary.poster, 2013-11-12 20:26:07]

*** Submitted:

Simplify bundle vis centering

It turns out that using a polygon centroid isn't quite what our eyes expected,
and also caused a bug when elements were away from the center mass of services. 
Using the bounding box gives more expected results.

I didn't add a test, because I argued to myself that this was a visual thing,
but I'm really lying to myself, and if you want to call me out on it, please
feel free to appeal to my better self. :-)

To QA, look at a lot of bundles, like those from "hatch", "jorge", and "gary". 
Then also look at the problematic one,
http://localhost:8888/sidebar/search/bundle/~makyo/mediawiki-scalable/5/media...
.  Compare it with the rendering in trunk (like on comingsoon) to see the
difference.

R=matthew.scott
CC=
https://codereview.appspot.com/25460043