WIP: Do not move to sent folder, see #1

[mpolitze]

As described in #1 the extension was copying incoming mails to the sent folder.

I added a chek to exclude common 'special' folders as specified by the type property.

To make editing a little easier I also included some boilerplate for type checking.

I hope this can be merged. Thank you!

[pklampros]

I generally don't disagree with having specific exceptions, but you seem to require a narrower case than I do. You see, I make thunderbird move all my sent messages into the folder that I'm responding to (there's an option in thunderbird itself) and tend to think of emails as by-topic rather than by-type (sent/received etc.). Looking at the exceptions you set, it seems weird to me that any email would find itself in -for example- outbox and then have a response.

However, every person has their own weird filing habits (myself included 😆), so I will happily accept this if you put it behind a setting!

P.S. and thanks for the type checking!

[mpolitze]

Thanks for the response!
My idea was to simply exclude "all" special folders defined in TBs API. I see that this is debatable.
I will find out how settings work in TB add-ons and make an update :)

[mpolitze]

I begin falling in love with TB add on development 😁

The settings page is there... but will run the code for a couple of days to check that everything turns out ok.

PS: I almost added the full typescript pipeline, but figured that would slightly overshoot the goal...