Size of the local covers in infos tab

[dcartron]

As i already have quite all the covers of my albums in the directories
with the music, i use them first. The problem is that some of them are
quite big, because if i normally resize them to 300x300 (the good size
for my mp3 player) somme are not.

And in the infos tab, the image is not resized at all, so all the text
is pushed out of the window!

It should be nice to be able to define the max size of this image, as
well as the smaller one on the left top.

[multani]

I proposed a possible fix as a comment on #77 (comment) which would make the cover size dynamic without resorting to an additional preference setting.