Started adding V1 to model
Wire things in order, e.g. first retina to LGN, then LGN to V1 etc.
Reordering of cells in Early Vision Model, so logically defining input sheets shows up before defining connections etc.
Use v1aff, lgnaff, lgnsurroundbuffer for bounding boxes of sheets
Simplified and unified calculations for spatial frequency sheets
Various renames
Use **params rather than explicit parameters in SheetInstantiator
Improved doc strings
Unified LGNAfferent with LGNAfferentSF ProjectionSpecification
Nicer formatting in ProjectionSpecification subclasses
Removed create_sheet in SheetInstantiator, do the former function inline