Use tailored user-agent in requests to API

[juhoinkinen]

It can be nice to know from API logs when Annif-client is used.

[juhoinkinen]

I was about to merge this, but now I'm getting this error again, which somehow at first time got solved by reinstallation with pip install -e .:

Demonstrating usage of AnnifClient

* Creating an AnnifClient object
Traceback (most recent call last):
  File "annif_client.py", line 115, in <module>
    annif = AnnifClient()
  File "annif_client.py", line 17, in __init__
    version = importlib.metadata.version("annif-client")

[juhoinkinen]

I was about to merge this, but now I'm getting this error again, which somehow at first time got solved by reinstallation with pip install -e .:

Demonstrating usage of AnnifClient

* Creating an AnnifClient object
Traceback (most recent call last):
  File "annif_client.py", line 115, in <module>
    annif = AnnifClient()
  File "annif_client.py", line 17, in __init__
    version = importlib.metadata.version("annif-client")

Switching to perform the import like from importlib import metadata somehow fixed the problem. But this was only needed for the application code, not for the tests... The situation is the same as described in this discussion.