One download at a time (lock file)

[aloralove]

Continue this task following #92 completion.

Add a lock file so only one person can download it at a time. Make sure to note this in the code. should be in own sub dir

https://www.putorius.net/lock-files-bash-scripts.html

• [x] add touch to create lock file before download
• [x] remove after download
• [x] remove when interrupt (ex: ctrl C)
• [x] add remove code to the clean up
• [x] check temp_dir folders are being removed
• [ ] test