Help the user write .gitignore files

[rlnsanz]

The user decides which files in the directory we automatically version or not (on every execution of a Flor experiment) with a .gitignore file. Since this file can be very important, we should provide some assistance in writing it.

1. We could provide default files
2. We could have a bash or python script that asks the user questions and uses the answers to generate a .gitignore file.
3. Some combination of the above

What if the user says we should ignore JSON files but Flor emits JSON logs that are necessary for its proper functioning.

• Create a special subdirectory that is exempt from the rules in the .gitignore file: every file in that subdirectory is versioned, regardless of the contents of .gitignore .