Improved plugins, better tests, gevent

Moved from Yapsy again (it is not flexible enough), now we use a
custom solution.
The activation and deactivation of plugins is asynchronous, so
that plugins that take a long time don't interfere with the rest.

tests/sleep_plugin/sleep.py

@@ -0,0 +1,10 @@
+from senpy.plugins import SenpyPlugin
+from time import sleep
+
+class SleepPlugin(SenpyPlugin):
+    def __init__(self, info, *args, **kwargs):
+        super(SleepPlugin, self).__init__(info, *args, **kwargs)
+        self.timeout = int(info["timeout"])
+
+    def activate(self, *args, **kwargs):
+        sleep(self.timeout)

tests/sleep_plugin/sleep.senpy

@@ -0,0 +1,8 @@
+{
+    "name": "Sleep",
+    "module": "sleep",
+    "description": "I am dummy",
+    "author": "@balkian",
+    "version": "0.1",
+    "timeout": "2"
+}