Removing natbib sourcing from `preamble.tex`.

Moving the natbib sourcing back into each of the manuscript files.
Also updating the bib style from `evolution` to `bmc-mathphys` for
dpp ms.
Adding `ifbmc` macros and updating dpp tables.

Adding `ifbmc` to `macros.tex`, and using it in `dpp-msbayes-tables.tex`
so that `rowcolors` is not used if the document class is `bmcart`.