standardize plot aesthetics

[Thomas Gilgenast]

basically we could just make all plotters call sns.set_style('ticks') and quickly attain a "default aesthetic" for lib5c plot subcommands

[Thomas Gilgenast]

major overhaul of counts/primermap parsing and plotting API

plotting API is now formalized in a new decorator: @lib5c.util.plotting.plotter

most plotters now follow this API, except for the old heatmap plotters and cluster heatmap plotters, as well as legacy plotters

primermap/counts parsing is now standardized in line with modules2016: only two functions are supported: load_primermap() and load_counts()

all tools have been updated to reflect this change

lib5c.tools.helpers.resolve_level() has been broken up into lib5c.tools.helpers.resolve_level() and lib5c.tools.helpers.resolve_primerfile() - this helper is only needed in a small number of tools

lib5c.tools.parents.level_parser has been broken up into lib5c.tools.parents.level_parser and lib5c.tools.parents.primerfile_parser - level_parser is used rarely while primerfile_parser is ubiquitous

this closes #23, closes #21, closes #18, closes #22, closes #11, and closes #9

→ <<cset f4e899afa042>>