Removed reqwest library.

The new API depends simply on POST and doesn't even require all the
header and cookie trickery the previous did. Furthermore, there are
a few small bugs in reqwest we would have needed to worry about,
just to implement a thin wrapper on top of it in order to be able
to POST.

All in all, the code that implements the exact functionality we need
is not much more complex than what we had for wrapping reqwest, so it's
hard to still justify its presence.
Parse duration for track command.
HAWK support