[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/util/popup.py

@@ -0,0 +1,58 @@
+"""Pop-up menus."""
+
+import logging
+
+try:
+    import Tkinter as tk
+except ImportError:
+    # python 3
+    import tkinter as tk
+
+import functools
+
+
+class menu(object):
+    def __init__(self, parent=None, leave=True):
+        if not parent:
+            self._root = tk.Tk()
+            self._root.withdraw()
+            self._menu = tk.Menu(self._root, tearoff=0)
+            self._menu.bind("<FocusOut>", self._on_focus_out)
+        else:
+            self._root = parent.root()
+            self._root.withdraw()
+            self._menu = tk.Menu(self._root, tearoff=0)
+            self._menu.bind("<FocusOut>", self._on_focus_out)
+        if leave:
+            self._menu.bind("<Leave>", self._on_focus_out)
+
+    def root(self):
+        return self._root
+
+    def menu(self):
+        return self._menu
+
+    def _on_focus_out(self, event=None):
+        self._root.destroy()
+
+    def _on_click(self, callback):
+        self._root.destroy()
+        callback()
+
+    def add_cascade(self, menuitem, submenu):
+        self._menu.add_cascade(label=menuitem, menu=submenu.menu())
+
+    def add_menuitem(self, menuitem, callback):
+        self._menu.add_command(
+            label=menuitem, command=functools.partial(self._on_click, callback)
+        )
+
+    def show(self, event, offset_x=0, offset_y=0):
+        try:
+            self._menu.tk_popup(event["x"] + offset_x, event["y"] + offset_y)
+        finally:
+            self._menu.grab_release()
+        self._root.mainloop()
+
+
+# vim: tabstop=8 expandtab shiftwidth=4 softtabstop=4