[Foodmasst] Fix with empty files / results

[robinschmid]

@mwang87 @ka-west

this should fix the issues. I added an argument to always succeed with the scripts - this way we will even output empty files if the input was empty.

The commit messages clearly state what changed. A few notes:

• write empty files instead of files with the string "EMPTY" in them
• I downloaded the metadata file from github to add it to this directory. This way we do not rely on GitHub being online to run foodMASST

[robinschmid]

Fixes #755