Fixes #59

Instead, the error is logged and the tray app will exit.

Fixes #44

Refers to #35

Fixes #64

Relates to #53

Refers to #55

Since the executable will be located in the service base directory it
makes most sense to check in the `var` subdir for the config by default.

Fixes #58

Fixes #51

Refers to #53

Fixes #56

Fixes #53

Fixes #55

Fixes #54

Refers to #50

That's the earliest place where setting up the mail logger is possible /
makes sense, so do it right then. Additionally, the check for SmtpHost
is redundant since it also done in the method called, so no need for it.

Refers to #50

Refers to #35