Improvements on the delete_seen_shows Python script (and installation improvements)

[bernardomaciel]

This PR contains a few improvements on the delete_seen_shows Python script. Namely:

• All logging goes to a file now
• Added dryrun flag that does not actually delete anything
• Other minor fixes (autopep8, Python conventions, typos, script description)

I also added a .gitgnore file.

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There are also two commits (the last two) that are intended to close #14. Sorry for putting the two things together... I should have used branches!

[bernardomaciel]

Changes done.