klippy: Allow each module to define their config sections

Create add_printer_objects() functions in the fan, heater, extruder,
and toolhead modules.  Create the necessary printer component objects
from this call instead of placing the code directly in klippy.py.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

klippy/toolhead.py

@@ -382,3 +382,6 @@ class ToolHead:
             self.reset_print_time()
         except:
             logging.exception("Exception in force_shutdown")
+
+def add_printer_objects(printer, config):
+    printer.add_object('toolhead', ToolHead(printer, config))