Get a context by name, create the default context if it does not exist

		Params:
			context_name (string):
				Context name

		Raises:
			KeyError:
				If the context name does not exist

		Returns:
			bubbler.Bubbler:
				Named context

def getContext(self, context_name = 'default'):
		"""Get a context by name, create the default context if it does not exist

		Params:
			context_name (string):
				Context name

		Raises:
			KeyError:
				If the context name does not exist

		Returns:
			bubbler.Bubbler:
				Named context
		"""
		if context_name == 'default' and 'default' not in self.contexts:
			self('default')

		return self.contexts[context_name]