Added config option for adding a default hashtag to AP posts. like name of your city.

This may need a little cleaning up, or may not even be wanted, but I wanted some way to always add a hashtag to the fediverse message but that doesn't show up in the original event data, so that automatically the name of my city would be tagged in the Mastodon toot or whatever and you wouldnt need to always put it in every event manually. "default_fedi_hashtag" is the option i came up with,added to to the config file. I suppose it might be even better if the option took an array of tags.