Add ElementBase.points to constructor and cache bounding boxes

Since points is a member variable of ElementBase it should be
created in the constructor.

This allows caching the bounding box for elementary objects
as well.
Merge pull request #5 from mabl/point_corrections

Add ElementBase.points to constructor and cache bounding boxes
When saving a layout, only cell names that are not alread unique are uniquified
Updated utils to deal with new division between reference and object elements of Cell
Use numpy when saving coordinates of Boundary and Path

Using numpy to scale, round and convert to integer is far
more efficient and even shorter in source code.
Merge pull request #9 from mabl/np_save

Use numpy when saving coordinates of Boundary and Path