Platform from dart:io cannot be used on the web for reasons. And this
way we get a fake File/Directory class which we can use for atleast
running the web version, even if it won't work.
The iOS updates keep getting rejected, and I think it's because
RevenueCat is taking too long to respond. Additionally, revenueCat
doesn't really give us anything useful as its receipt validation isn't
perfect, and I've had to roll my own.
Plus from a privacy point of view, this is better as we are no longer
talking to any third party service.
This has so far only been tested on iOS
With this 'txt' files are now read and written. However, they don't have
any metadata so they don't show up correctly in the sort order and
currently the Markdown Editor is still available for them.
Related to #55