Info msg for missing config; strip email whitespace; mailinglist defaults

 Random fixes for issues I ran into when configuring the notifier with gitolite, but should be applicable most places.

* Allow for info message if the config.yml specified isn't found. It seems to be okay to not have a config file, but at least warn.
* I had whitespace between email addresses in the mailinglist config variable and the email didn't send to the second address.Stripping whitespace after splitting helps.
* Added a configuration variable to choose whether to prefer the git config hooks.mailinglist variable over the one in the config.yml. I'd like to use the git one if defined in my gitosis.conf but fallback to the one in the config otherwise. Not sure if this would be for everyone, but it helps for me.