rendering: Simplify Cairo context usage, remove unneeded calls.

Moved Cairo context usage to Rust, and rearranged ctx setup (position) to happen in one place.

Removed render calls that were overwritten on each draw call anyway.

src/lib.rs

@@ -1,5 +1,8 @@
 #[macro_use]
 extern crate bitflags;
+extern crate cairo;
+extern crate cairo_sys;
+extern crate gdk;
 extern crate gio;
 extern crate glib;
 extern crate glib_sys;
@@ -14,6 +17,7 @@ extern crate xkbcommon;
 
 mod action;
 pub mod data;
+mod drawing;
 pub mod float_ord;
 pub mod imservice;
 mod keyboard;