[Feature request] Avoid login in source site when using exported file

[ngosang]

If all required information is in the exported file. Why we have to perform login in the source site?
In best case it takes time, in worst case there is an error and you can't import.

$ python3 transfer_ratings.py --s trakt -f /home/kizar/repositories/RatS/RatS/exports/20210326181821_Trakt_mod.json -d letterboxd
===== Trakt: performing login
===== loaded 2 movies from /home/xxx/repositories/RatS/RatS/exports/20210326181821_Trakt_mod.json
===== Letterboxd:  ...

[StegSchreck]

Right, this was a workaround at the beginning to initialize the source Site object. I agree that it would be cleaner to separate the initialization from the login. Thanks for your input!