server: Wrapping functions with return values as interface requests

Edited-by: Pier Luigi Fiorini <pierluigi.fiorini@gmail.com>
server: Remove the Transient, Fullscreen and Maximized surface types

They are instead now states of TopLevel surfaces.

Edited-by: Pier Luigi Fiorini <pierluigi.fiorini@gmail.com>
server: Add xdg_shell support.

It still misses a couple of things, but the main things are implemented.

Edited-by: Pier Luigi Fiorini <pierluigi.fiorini@gmail.com>
server: Don't create window objects for transient surfaces

Edited-by: Pier Luigi Fiorini <pierluigi.fiorini@gmail.com>
server: Don't show transient surfaces in the scale effect

Edited-by: Pier Luigi Fiorini <pierluigi.fiorini@gmail.com>
server: Fix setting a surface transient

Edited-by: Pier Luigi Fiorini <pierluigi.fiorini@gmail.com>
server: Set a surface active on creation

Edited-by: Pier Luigi Fiorini <pierluigi.fiorini@gmail.com>
server: Send focused state
server: Update according to latest Weston changes

Edited-by: Pier Luigi Fiorini <pierluigi.fiorini@gmail.com>