Provide old Filesystem view as an option

In QtCreator 4.5.0 beta 1 the Filesystem view panel on the left has been changed to a tree view. This is inconvenient for different reasons:

• There appears lots of space to the left of the file names for files deep in the directory structure. One has to scroll right to see the file names every time the current file is changed (I have Filesystem view synchronized with the editor, and the horizontal position of the view is reset to the leftmost position when the current file is changed).

• In order to find a file in the filesystem one has to do a lot of scrolling (i.e. first scroll up or down to the directory containing the file, then select the file). The old interface was easier to navigate because most of the time you would click through the directory structure up and then down, and doing so usually did not require a lot of scrolling and searching for the file/directory you want.

Overall, I much prefer the old interface over the new one and would like it to be available as an option. The tree view is just terrible for navigating large projects with deep directory structure.

One place where the old interface could be improved is finding the directory to open the file in. It would be nice to have a drop down field that would display a tree view of directories above the current directory so that one can easily navigate N levels up. The file list should still remain a normal list of files/directories in the current directory. I'm not requesting this improvement as part of this ticket though.