Google Sheets import

[Marx2]

There are plenty of google sheets portfolio trackers, and many people use it (me too, thousands of transactions). It's also quite easy to connect with such a sheet, you just need Google API credentials and sheet identifier.
Currently I don't want to abandon usage of Google Sheets, as I've built a lot of charts there. I'm also sure not all my country specific stocks are covered, so import would not succeed fully. It is also more complicated, because first I need to copy-paste from google sheets into Excel, then save as its proprietary format, then manually import in investbrain. I'm even not sure if it's possible to import same file twice and there will be no duplicates.

So the idea is to:

1. build in Google Sheets a sheet with format already defined by investbrain (tab names, columns, formats)
2. put somewhere (properties, envs, user profile) credentials and identifier of sheet
3. have a button "sync with google sheet"

If the format of sheet will be consistent with already implemented Excel import, it should not be so hard to implement it. The real tricky part is to make it incremental, not to end up with duplicates