stretch filename field

The current file table has empty space on the right. This makes selections look silly as they do not go all the way to the right.

There are four possible fixes ot this:
1) add an empty column to the right, and stretch that
2) stretch Filename column
3) stretch Size column
4) stretch Available column

Adding an extra column seems silly. Stretching Filename column makes sense because filenames may sometimes be long. Stretching Size column doesn't imo make sense in any case. Stretching Available column makes sense only because QT provides a boolean value for stretching last column. I think we should eventually find out a way for stretching the filename column.