Add a "Create project" feature

[danielbsig]

It should be possible for the user to select "File" - "New Project..." and get presented with at least one option: "C++ console project", possibly an empty one, possibly one which prints out "Hello world".

For this, we need to rethink how files are presented in the file window on the left. Currently, all files are displayed, but this would have to change.

[danielbsig]

Note: a project should have "Project settings", where we can control the flags passed to g++, in a graphical way (i.e. the user should not need to learn the parameters to g++.