[core] restructure to allow PIP packaging

OK - so I have to admit I *hate* the fact that PIP seems to require a
subdirectory named like the library.

But since the PIP package is something really nifty to have (thanks to
@tony again!!!), I updated the codebase to hopefully conform with what
PIP expects. Testruns so far look promising...

bumblebee_status/modules/contrib/yubikey.py

@@ -0,0 +1,41 @@
+# pylint: disable=C0111,R0903
+
+"""Shows yubikey information
+
+Requires: https://github.com/Yubico/python-yubico
+
+The output indicates that a YubiKey is not connected or it displays
+the corresponding serial number.
+
+
+contributed by `EmmaTinten <https://github.com/EmmaTinten>`_ - many thanks!
+"""
+
+import yubico
+
+import core.module
+import core.widget
+import core.decorators
+
+
+class Module(core.module.Module):
+    @core.decorators.every(seconds=5)
+    def __init__(self, config, theme):
+        super().__init__(config, theme, core.widget.Widget(self.keystate))
+        self.__keystate = "No YubiKey"
+
+    def keystate(self, widget):
+        return self.__keystate
+
+    def update(self):
+        try:
+            self.__keystate = "YubiKey: " + str(
+                yubico.find_yubikey(debug=False).serial()
+            )
+        except yubico.yubico_exception.YubicoError:
+            self.__keystate = "No YubiKey"
+        except Exception:
+            self.__keystate = "n/a"
+
+
+# vim: tabstop=8 expandtab shiftwidth=4 softtabstop=4