Automatically calculate the rows number in order to fit the toobar height

[lypwig]

When we change the toolbar height, the icons size remains the same, as well as the number of rows, both defined in options. This action only change the space between icons, which is not really interesting:

I suggest to remove the rows number option in the preferences, and automatically calculate this based on the toolbar height, ie:

user moves cursor down, then tadaaa!