Use .timer_setup() to setup timer, fix error from cffi markup renderer

1. In qtile-0.9.1 .timeout_add() must be run after ._configure(). In qtile-0.8.0
   .timer_setup() is not run automatically.
2. New pango markup renderer (qtile-0.9.1) is not accepting unicode() objects,
   only str() ones as it converts them to cffi `char *`.

Fixes #1313

powerline/bindings/qtile/widget.py

@@ -15,15 +15,16 @@ class QTilePowerline(Powerline):
 class PowerlineTextBox(TextBox):
 	def __init__(self, timeout=2, text=' ', width=CALCULATED, side='right', **config):
 		super(PowerlineTextBox, self).__init__(text, width, **config)
-		self.timeout_add(timeout, self.update)
 		self.side = side
+		self.update_interval = timeout
+		self.did_run_timer_setup = False
 		powerline = QTilePowerline(ext='wm', renderer_module='pango_markup')
 		powerline.setup(self)
 
 	def update(self):
 		if not self.configured:
 			return True
-		self.text = self.powerline.render(side=self.side)
+		self.text = self.powerline.render(side=self.side).encode('utf-8')
 		self.bar.draw()
 		return True
 
@@ -33,6 +34,11 @@ class PowerlineTextBox(TextBox):
 	def cmd_get(self):
 		return self.text
 
+	def timer_setup(self):
+		if not self.did_run_timer_setup:
+			self.did_run_timer_setup = True
+			self.timeout_add(self.update_interval, self.update)
+
 	def _configure(self, qtile, bar):
 		super(PowerlineTextBox, self)._configure(qtile, bar)
 		self.layout = self.drawer.textlayout(
@@ -43,6 +49,7 @@ class PowerlineTextBox(TextBox):
 			self.fontshadow,
 			markup=True,
 		)
+		self.timer_setup()
 
 
 # TODO: Remove this at next major release