Check for existing config and don't process if not new

[pjbull]

If we change the command, you could end up with multiple versions in your config file.

https://github.com/drivendataorg/nbautoexport/blob/master/nbautoexport/nbautoexport.py#L97-L103

• We should include the version number in the command initialize so that we can compare
• If the installing version number > one in config, we should remove that version and replace with the new one.

[jayqi]

The above link doesn't make sense anymore, since the lines have since moved around. Here is a permalink to the correct source code:

nbautoexport/nbautoexport/nbautoexport.py

Lines 97 to 103 in 65b3dc8

	command = """# >>> nbautoexport initialize >>>
	try:
	from nbautoexport import post_save
	c.FileContentsManager.post_save_hook = post_save
	except:
	pass
	# <<< nbautoexport initialize <<<"""