Navbar Logo - Be able to provide a different alt text for the logo instead of the site shortname

[danowar2k]

Is your feature request related to a problem? Please describe.
Our current site shortname maybe be something like "Moodle" or just "moodle-pruefungen". That is used for the navbar logo as the alt text for the image. Shouldn't the alt text for an image describe what the image is showing?
Our logo image would rather need an alt text like "Logo der FernUniversität Hagen".

Describe the solution you'd like
As an admin I would like to be able to change the alt text for the navbar logo from the default site shortname if I want. To be able to do this I would like a setting near the logo image setting with which I could override the alt text for that logo image.

Describe alternatives you've considered
Locally we'll currently do this by changing the alt text after the fact with Javascript. It would probably be better in core, where the problem originates.
If the templates would be a bit more split up so that the navbar logo code was in its own template, we'd have an easier way to just replace the text.

[danowar2k]

Looks like the other half of this was done earlier: #565 ;-)