local support modules should be either absorbed or moved into a package

currently code relies on ambiguous (looks global but is local) imports:

```python
from lookup_url import lookup_url
...
from globusclient import GlobusClient
from annexremote import Master
from annexremote import ExportRemote
from annexremote import SpecialRemote
from annexremote import RemoteError, ProtocolError
```

those files cannot be deployed (installed) on their own, so either would need to be moved into some local "proper package" (e.g. `git_annex_remote_globus` ;) ) or just absorbed within `git-annex-remote-globus` . In the former case, even the `git-annex-remote-globus` code could pretty much be moved into the package (e.g. as `git_annex_remote_globus/cmd.py`) and the actual `git_annex_remote_globus` would be just having the `__main__` portion.
That would make it easier to (eventually) establish `git_annex_remote_globus/tests` which would test functionality within that cmd.py somehow

Start by inspecting the current imports of lookup_url, globusclient, and annexremote and how git-annex-remote-globus is installed or deployed. Compare the proposed package layout, including git_annex_remote_globus/cmd.py and git_annex_remote_globus/tests; done means the support code is installable without ambiguous local imports and has a viable location for tests.

Written by the indexing model from the issue text.