FEAT: qiime tools show-types and qiime tools show-formats commands

[colinvwood]

Added two commands to show the available semantic types and importable and exportable formats for a qiime deployment.

Will replace the functionality of the qiime tools import --show-importable-types and qiime tools import --show-importable-formats commands.

Additionally:

• descriptions are given of each semantic type or format when available
• semantic types or formats can be subsetted to only those of interest
• a --tsv flag is available

Motivated by #289.

[gregcaporaso]

Hey @colinvwood, I haven't reviewed this in any detail, but I think it's worth removing the --show-importable-* functionality from qiime tools import ... in this PR too. I think the best way to do this is, if the user provides one of those flags, print a note saying that that functionality is now accessible instead through the new command and then exit (without printing the types/formats).

[gregcaporaso]

Hey @colinvwood, I have some requests for changes on this PR. It might look like a lot, but they're all pretty minor so I think this should be relatively quick to address. Let me know if you have any questions.

[colinvwood]

Not sure why the cache test is failing, maybe @Oddant1 can weigh in?

[gregcaporaso]

Looks good to me, thanks for the updates @colinvwood!

[Oddant1]

lgtm