Fix --help to show our extra options (#24)
Handle --version locally

Fixes the following bug:

1. Launch gtimelog
2. Run gtimelog --version in a new terminal
3. Expect the version to show up in the new terminal
Handle --sample-config locally

Fixes the following bug:

1. Launch gtimelog
2. Run gtimelog --sample-config in a new terminal
3. Expect the message about the config being written to show up in the
   new terminal

(Actually, I believe in older GtkApplication-based implementation both
--version and --sample-config would be simply ignored if GTimeLog were
already running in the background.)
Fix --debug output when GTK completion was disabled

It would print 'disabled' on a line of its own instead of
'GTK completion: disabled'.  Because I keep forgetting that ternary-if
has higher precedence over %.