do not require samples tsv for assembly-based workflows

[bluegenes]

(to do)

Right now, tsv file input is required whether or not we're using the reads (e.g. annotation does not require reads). This file is parsed directly in the snakefile.

To fix: in Snakefile, check all workflows within the config to see if any contain read extensions, meaning that they work on reads. If yes, parse the samples.tsv. Then add a check into run_eelpond to exit if the config doesn't contain either samples or assemblyinput.

[bluegenes]

manage samples via the get_data utility and params. Only look for/ use samples file if config.yml contains:

get_data: 
  samples: tsv_file

in snakefile, only read in the samples file if get_data params are present/provided. This should also be checked/ managed by the high-level inputs, err checking function (#110)