Switch qtclient to common static library

Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
Switch server to common static library

Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
Add common.pro project file for common static library

The common code gets linked into a static library that qtclient and
server can use.

Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
Add top-level project file

Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
Update README with new subdirectory layout

Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
Update README with mxe cross-compiler information

The mingw-cross-env project has been renamed mxe.  Update the build
instructions.

Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>