[modules/layout] add a new - generic - layout module

Add a new module "layout" that will eventually evolve into the only
keyboard layout module.

Right now, it uses an external binary (get-kbd-layout) to determine the
layout of a keyboard device (because I did not manage to call libX11
with ctypes correctly).

see #788
see #790

bumblebee_status/modules/core/layout.py

@@ -0,0 +1,39 @@
+# pylint: disable=C0111,R0903
+
+"""Displays the current keyboard layout
+
+Parameters:
+    * layout.device: The device ID of the keyboard (as reported by `xinput -list`), defaults to the core device
+"""
+
+import re
+
+import core.widget
+import core.module
+
+import util.cli
+
+from bumblebee_status.discover import utility
+
+class Module(core.module.Module):
+    def __init__(self, config, theme):
+        super().__init__(config=config, theme=theme, widgets=core.widget.Widget(self.get_layout))
+
+        self._cmd = utility("get-kbd-layout")
+        keyboard = self.parameter("device", None)
+        if keyboard:
+            self._cmd += " {}".format(keyboard)
+
+    def get_layout(self, widget):
+        result = util.cli.execute(self._cmd, ignore_errors=True)
+
+        m = re.search("([a-zA-Z]+_)?([a-zA-Z]+)(\(([\w-]+)\))?", result)
+
+        if m:
+            layout = m.group(2)
+            variant = m.group(3)
+            return layout if not variant else "{} {}".format(layout, variant)
+
+        return "n/a"
+
+# vim: tabstop=8 expandtab shiftwidth=4 softtabstop=4