feature-table group should generate new metadata

[antgonza]

Improvement Description && Current Behavior
The collapse methods do not generate a mapping file so there is no automatic way of using the resulting table without by hand creating a new mapping file

Proposed Behavior
The simplest behavior will be to generate a single column metadata file with the summarized categories as sample names. However, it will be nice if (for the examples, let's assume that we have unique samples from different cities):

• we could add all unique values for those categories from the original metadata file: if summarized by city and we had unique zip/area-codes add them to the new mapping file
• we could have a list of possible values: if we summarize by state, add all the possible values of city