Resize the "Subject" column when the window is resized

[Feuermurmel]

Currently, changing the width of the window does noting helpful to the widths of the columns. Making the window wider will just leave the columns as-is, making it smaller will just shrink the Short SHA column to the width of a single character.

I'd suggest that all columns should keep their width, except for the Subject column, which should use all the remaining space.