Preference: Autoload tags if file + .tags extension exist

[phastmike]

Add option to autoload tags file if when open a file and a tags file with the same name + the tags extension exist

[phastmike]

Need to decouple load_tags() action from the tag loading. We just need a filename. While in the action we provide the load file popup interface in autoload we already the filename. Just need to append the .tags suffix and check if the file exists, if so, load it. Will be related to the feature of keeping track of tags add/remove/edit - exiting without saving tags warning.