Fixed camera settings

Since splitting the camera config into a separate YAML file, we've broken
the ability to change the camera's configuration via the API (or at any time
except when the camera is set up, I think).  This (mostly) fixes that, though
I get type errors that I've had to work around (e.g. when setting
shutter_speed), see `pi.py`

openflexure_microscope/camera/base.py

@@ -125,6 +125,14 @@ class BaseCamera(object):
         self.images = self.load_capture_db(self.images_db)
         self.videos = self.load_capture_db(self.videos_db)
 
+    def apply_config(self, config):
+        """Update settings from a config dictionary"""
+        self.config.update(config)
+
+    def read_config(self, config):
+        """Return the current settings as a dictionary"""
+        return self.config
+
     def __enter__(self):
         """Create camera on context enter."""
         return self

openflexure_microscope/camera/pi.py

@@ -184,12 +184,17 @@ class StreamingCamera(BaseCamera):
                                 set_digital_gain(self.camera, value)
                             elif key == 'analog_gain':
                                 set_analog_gain(self.camera, value)
+                            elif key == "shutter_speed":
+                                self.camera.shutter_speed = int(value)
                             else:
                                 setattr(self.camera, key, value)  # Write setting to camera
 
                 # StreamingCamera parameters (applied via StreamingCamera config)
                 for key, value in config.items():  # For each provided setting
-                    if key != 'picamera_settings':  # We already handled this
+                    if key in self.config.keys():
+                        if key != 'picamera_settings':  # We already handled this
+                            logging.warn("{} is not in the streaming camera settings dictionary - adding it.")
+                            #continue #TODO: filter settings somehow?
                         logging.debug("Setting parameter {}: {}".format(key, value))
                         self.config[key] = value