Rahul's changes

[rahulk29]

[dan-fritchman]

Per yesterday 11/3's meeting with @growly & @aviralpandey:

• Gotta support VLSIR, it's our primary on-disk format. Not just GDSII.
  • A good test for these changes would be: run the command-line tools gds2proto and proto2gds back-to-back, and (at least "semantically") compare the round-tripped GDS files.
• We've all pretty much admitted that as little as we like them, we probably need GDSII-style "layered" or "3D located" text labels.
  • Adding these to layout.raw.LayerShapes, and then adding the code to import and export them, would probably do it
• We did not review the layer-manager changes, and should before merging.