dumb move of everything context-related into new package
roughly chop context package into separate files. tests not touched, can't quite bear it right now
Refactor the UserManager and commands.

This branch adds consistency to the UserManager.
Primarily around the use of tags to pass the usernames.
Also untangles the API client from the server that was
there with the user manager structs being defined in the
apiserver package (not params).

The commands have been hooked up, and tested manually.

There were several clear changes needed when testing:
 * until we have multiple environments, creating a user
   should cause that user to have access to the environment
 * when adding a user, we should always write out the jenv
   file (until the user is able to login and see themselves)
 * the remove user command has been renamed to disable,
   as it wasn't removing the user at all (this is still todo)
Many changes due to review comments.

Deactivated renamed throughout.
Client side user manager now deals in strings.
Commands moved into user directory.
Fix spelling mistake.
Final review tweaks.
And fix the test.
Merge pull request #905 from howbazaar/user-manager-tag-redux

Refactor the UserManager and commands.

This branch adds consistency to the UserManager.
Primarily around the use of tags to pass the usernames.
Also untangles the API client from the server that was
there with the user manager structs being defined in the
apiserver package (not params).

The commands have been hooked up, and tested manually.

There were several clear changes needed when testing:
 * until we have multiple environments, creating a user
   should cause that user to have access to the environment
 * when adding a user, we should always write out the jenv
   file (until the user is able to login and see themselves)
 * the remove user command has been renamed to disable,
   as it wasn't removing the user at all (this is still todo)
Update errors usage.
Merge pull request #937 from howbazaar/update-errors

Update errors usage.

Update to the latest juju/errors.

Old Contextf and Maskf replaced by DeferredAnnotatef.
Merge pull request #923 from fwereade/uniter-extract-hook-context

Uniter: extract hook context

pull hook context out into its own package, and split it up into a bunch of files organised roughly by intent. There's nothing clever here, but it helps make clear just how parlous the state of the testing here has become, and it feels like a necessary step towards sanity in the uniter package.