Add Exec lines in services files for backword compatibility reasons

[bhush9]

For non-kdbus, non-systemd systems

[eliasp]

Under the assumption, this doesn't cause any race-conditions for DBus activation on kdbus systems, I'm merging it.

We'll have to test and see whether it works as expected. IIRC I intentionally dropped the Exec= lines as I wasn't sure whether back then whether this would cause DBus activations to still execute the binary instead of triggering the service, but I believe this is properly handled nowadays by systemd-bus-proxyd.

[AnAkkk]

This is missing org.kde.kded5.service and org.kde.kwalletd5.service. I had to remove these two as well since they already existed.