ToDo plugin - add support for project files (qmake, cmake)

Task management for project files

I've noticed that inside the project files for qmake (`pro` file) and cmake (`CMakeLists.txt` file) adding a task entry (`TODO`, `FIXME` etc.) that can be viewed through the To-Do Entries view is not possible. In `CMakeLists.txt` there seems to be at least some highlighting support.

If you work on a rather complex project file having the ability to properly manage tasks would allow increasing the productivity in such scenarios.