APy Service

I tried to upgrade my manual installation to ubuntu packaging as instructed in README:

```
$ wget -qO- https://apertium.projectjj.com/apt/install-nightly.sh | bash
$ apt-get install apertium-apy
```

The resulting server doesn't seem to be functional:
```
flammie@flammie:~$ sudo systemctl start apertium-apy
flammie@flammie:~$ sudo systemctl status apertium-apy
● apertium-apy.service - Translation server and API for Apertium
Loaded: loaded (/lib/systemd/system/apertium-apy.service; enabled; vendor preset: enabled)
Active: inactive (dead) (Result: exit-code) since pe 2019-08-16 08:53:43 EDT; 5s ago
Docs: http://wiki.apertium.org/wiki/Apertium-apy
Process: 28320 ExecStart=/usr/bin/apertium-apy /usr/share/apertium/modes (code=exited, status=1/FAILURE)
Main PID: 28320 (code=exited, status=1/FAILURE)

elo 16 08:53:42 flammie.name systemd[1]: apertium-apy.service: Unit entered failed state.
elo 16 08:53:42 flammie.name systemd[1]: apertium-apy.service: Failed with result 'exit-code'.
elo 16 08:53:43 flammie.name systemd[1]: apertium-apy.service: Service hold-off time over, scheduling restart.
elo 16 08:53:43 flammie.name systemd[1]: Stopped Translation server and API for Apertium.
elo 16 08:53:43 flammie.name systemd[1]: apertium-apy.service: Start request repeated too quickly.
elo 16 08:53:43 flammie.name systemd[1]: Failed to start Translation server and API for Apertium.
```
The problem seems to be with the locale but I think the startup scripts should handle setting the correct locale?

It seems that the startup script tries to set C.UTF8 locale but somehow doesn't work, using /etc/default/apertium-apy fixed it:
```
flammie@flammie:~$ cat /etc/default/apertium-apy
LC_ALL=C.utf8
```

Reproduce the failure with the README installation commands and inspect /lib/systemd/system/apertium-apy.service, the startup script, and /etc/default/apertium-apy. Determine why the service does not receive a working C.UTF8 locale; it is done when the packaged service starts without manually creating that configuration.

Written by the indexing model from the issue text.