Remove `Command.globs` method

It is no longer being used.
Get relative paths of directories to ignore

Use `Pathname#realpath` to get absolute paths so that
`Pathname#relative_path_from` will not raise an exception. Also add the
config files to this list.
Refactor logic into Command class. Add tests.
Merge pull request #2459 from ivantsepp/watch_ignore_files
Update history to reflect merge of #2459 [ci skip]
Add parens to issue #. [ci skip]