Make an ability switching to plain file view for cmake-servermode project

Creating issue after mailing list thread:

http://lists.qt-project.org/pipermail/qt-creator/2017-May/006537.html

After upgrading to 4.3 I was disappointed, that new CMake projects has a large plain list of targets, without folders, without preserving file structure.

Project navigation is mostly useless now - yes, I have "filesystem view", but it very unpleasant to switch between two views to make operations with project (filesystem view show all files in tree - which is not convenient).

I suggest you to create mode "plain file tree" for cmake project, which shows just the same files, but without target grouping, just as with cmake 3.6 now.