cloud storage

[Dirk Hohndel]

I just pushed a bunch of changes to the cloud storage.

This should be ready for testing now.

The email / password / pin logic is unchanged to what I explained a few
days ago. Except that now not saving the password locally actually works
as expected :-)

There is a new checkbox for automated sync in the background. This may
need a different name - all it means that if you save, it tries to then
push the changes to the remote.

I also implemented the teapot protocoll. libgit takes forever to realize
that it can't connect to the remote. We now figure that out in a couple of
seconds BEFORE we try to connect with libgit2.

And if you are using a bunch of patches to libgit2 that haven't landed in
libgit2 master, yet, then all this even works across an http proxy. And in
my limited testing having the code there doesn't break anything with the
libgit version that is used by the build script. It just annoyingly fails
behind a proxy (and here the teapot protocol fails to help because that
does use the proxy).

I'd love to see people test the code. It's a bit unintuitive to use right
now (basically you need to create the account, then load from the cloud
server (which should get you an empty file), then import what you want to
store there and save (or quit). There are a lot of rough edges, oddities
in the UI, etc. But the basics should work - cloud storage for Subsurface
:-)

Linus, if you have a moment I'd love for you to review the changes I made
to save-git.c and git-access.c - I think they all make sense but that
doesn't mean that I'm right.

Have a good weekend, everyone!

/D