Use stable hard-coded path in service file for Lomiri

[jonnius]

Currently, the ExecStart field in the service file on Ubuntu Touch / Lomiri contains the app version. This breaks the service on each update. This PR changes the path to a hard-coded and stable one.

[rinigus]

I don't get it - why is QCoreApplication::applicationFilePath not the same path in UT? What is it then? Maybe we should fix that...

[jonnius]

It returns the correct path (/opt/click.ubuntu.com/osmscout-server.jonnius/<version>/usr/bin/osmscout-server). The problem is that this path changes with each update. So we are storing a rather volatile path into the persistent systemd service file.

There is a symlink current always pointing to the current version. That is what I am using in this workaround, providing a stable path over versions.

Without this workaround I see two alternatives:

• Rewrite the systemd files on app start. Only helps if the user actually opens the GUI after updating.
• Explain to the user that he needs to disable and re-enable automatic server activation after each update.

[rinigus]

I see. No, we can surely add this workaround. Merging.