Serious tidy-up of init, add isp_blocks

The initialization routine was getting stupidly long and overly complex.
This splits it into a series of separate methods each with a
(reasonably) well defined purpose. It also adds the isp_block attribute
and init parameter.

Author: waveform80

docs/api_camera.rst

@@ -18,7 +18,7 @@ the library (excepting the contents of :mod:`picamera.array`)::
 PiCamera
 ========
 
-.. autoclass:: PiCamera(\*, camera_num=0, stereo_mode='none', stereo_decimate=False, resolution=None, framerate=None, sensor_mode=0, led_pin=None, clock_mode='reset', framerate_range=None)
+.. autoclass:: PiCamera(\*, camera_num=0, stereo_mode='none', stereo_decimate=False, resolution=None, framerate=None, sensor_mode=0, led_pin=None, clock_mode='reset', framerate_range=None, isp_blocks=None)
 
 
 PiVideoFrameType