Removed deprecated `Status()` function

[zeisss]

The Client.Status() function can be seen as deprecated, since the StatusAll() and StatusUnit() functions provide much more information.

[zeisss]

@teemow I am a bit confused about the changes with the http-api, as you said Status wasn't supported there yet.

Thus this ticket to discuss the future design goal ;)

my points of confusion:

1. The cli has two ways for the status: Status and UnitStatus. As specified in this ticket, I favor UnitStatus() over Status() - do we want this also to be in the interface like this?
2. As far as I can tell from the docs (alpha-0.1) and the code, we should have everything (loaded, active, sub status, description, machine) we need to construct our UnitStatus object.
   If you look at the cli implementation of Status(), it just iterates over the output of fleetctl list-units and checks the sub column status.

My UnitStatus is more or less equal to your Get() which returns a struct from the original fleet repository. Do we want that? Or should we go with our own type?

[zeisss]

I exposed the UnitStatus() now with #4 to implement the status feature.

[zeisss]

cc @zyndiecate

[xh3b4sd]

+1 own types. A user should not be forced to import yet another package for such type definitions of a package we use internally.