Pure LaTeX version of manuscript including panorama multi-fig

This is a pure LaTeX version located, self-contained, in `./latex`, which will not update with the other .rst -> TeX system.

Composing directly in LaTeX, IMHO, is appropriate at this time for the necessary subtle tweaks required at this stage. Certain features of this conversion were simply not possible without doing so (see: Panorama multi-fig, line break hints).

It uses one main document `latex/skimage.tex` with a modular approach, including sections of the paper from separate `.tex` files with `\input`. This is similar to how the current structure operates. Before it builds, it regenerates all paper figures and then looks in `./output/skimage` for graphics files.

Also added are two new Make targets: `make latex` and `make viewtex` which should automate everything.

Notable features:

* Incorporates Juan's updated references
* Based on the original pre-print
* Uses pythontex for elegant code typesetting (shipped in TeX Live 2013/MacTeX)
* Solves the panorama multi-fig example