[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/core/error.py

@@ -0,0 +1,33 @@
+# pylint: disable=C0111,R0903
+
+"""Shows bumblebee-status errors"""
+
+import platform
+
+import core.module
+import core.widget
+import core.event
+
+
+class Module(core.module.Module):
+    def __init__(self, config, theme):
+        super().__init__(config, theme, core.widget.Widget(self.full_text))
+        self.__error = ""
+        self.__state = "critical"
+
+        core.event.register("error", self.__set_error)
+
+    def full_text(self, widgets):
+        return self.__error
+
+    def __set_error(self, error="n/a", state="critical"):
+        self.__error = error
+        self.__state = state
+
+    def state(self, widget):
+        if self.__error:
+            return [self.__state]
+        return []
+
+
+# vim: tabstop=8 expandtab shiftwidth=4 softtabstop=4