klippy: Rename try_load_module() to load_object()

Rename try_load_module() so that it uses consistent naming for
"printer objects".  Change the function to raise an error by default
if the specified module does not exist.

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

klippy/extras/heater_generic.py

@@ -5,5 +5,5 @@
 # This file may be distributed under the terms of the GNU GPLv3 license.
 
 def load_config_prefix(config):
-    pheaters = config.get_printer().try_load_module(config, 'heaters')
+    pheaters = config.get_printer().load_object(config, 'heaters')
     return pheaters.setup_heater(config)