Cleanup torrent model item

This patch is doing 2 things.

First. Currently torrent model item has two mutable members: icon and color. They are changed when status() is queried. If status() is not queried they are not changed. This is bad that content of one column depends on querying of other column.

Second. QColor was created by string. This is not very slow, but slower than creating it by Qt::GlobalColor. I used Qt::GlobalColor. The only problem is that orange is not present in GlobalColor, so I just used it's RGB values.