Implement a better way to open metacatalog CONFIGFILE

[AlexDo1]

Loading and reading the metacatalog CONFIGFILE is currently done in the following way:

metacatalog/metacatalog/ext/__init__.py

Lines 56 to 61 in 1219f7f

	from metacatalog import CONFIGFILE
	import json
	import importlib
	with open(CONFIGFILE, 'r') as f:
	config = json.load(f)

It would be nice to read and get values from CONFIGFILE directly without the need of the with open(CONFIGFILE) as f block.