Use the log_path from the confguration

[plasorak]

Requires DUNE-DAQ/confmodel#51

This fixes: #257 and #200 (change the log file extension).

This uses the following logic:

1. Applications will log to their log_path (defined in the Application schema).
2. If above is not set, the applications will log to their Session's log_path.
3. If above are not set, the applications will log to PWD.

In cases 1. and 2., the log will be non overwriting (i.e. they will have a timestamp assigned to them). In the case 3. overwriting logs is controlled by the boot's --override-logs/--no-override-logs switch.

Note that there is logic to check that the path exists if you are running on localhost:
Say you configured your log_path to /bananas/cucumbers/potatoes, drunc will only be able to say whether this path exists (and therefore thrown a reasonable exception) if you are running on localhost.

There is no check if that path is writable, or if the disk has space.

[PawelPlesniak]

LGTM