ui: Make the summary output logdir clickable in most TTYs.

It would be even easier for most users of our graphical desktop
environment to look at log files if they could click on the log dir.

By prefixing the log dir path with file://, now they can (in Konsole and
I'm sure most others).

I thought about implementing OSC8 support (TTY escape codes for
hyperlinks) but we don't support that in Konsole and I'm not sure how
many other TTYs are commonly used in Plasma.