Lstag Subcommand: Add flag to list all tags, not list files

[joemahmah]

The current lstag subcommand will only list the tags which were specified as arguments. A flag (all, -a) should be added that will list all tags (and ignore the arguments). Given that there may be tags with a large numbers of associated files, the subcommand should also have another flag (count -c) which will list the number of files associated with the tag rather than listing the file.