Resize and position layer relative to artboard

What this does:

 - Keeps the original name of the group, instead of adding ' 2'.
 - Resizes the group relative to the destination artboard.
 - Positions the group within and relative to the destination artboard.

I've tested with text within the group, which works as well.

As far as I can see, this closes #2 and #3.

![screenshot 2014-06-26 21 59 35](https://cloud.githubusercontent.com/assets/67565/3404039/ae8c323e-fd6c-11e3-99a9-9c703cb60c3a.png)