Add helper for running thor tasks with remote.thor

[mattbrictson]

Thor is an alternative to rake for writing command-line scripts in Ruby. It is built into Rails and maintained under the Rails GitHub organization.

In a Rails project, you can place .thor files under lib/tasks/ (for example). Similar to Rake, you can run thor -T to see a list of commands, and thor COMMAND to run a command defined in one your .thor files.

Thor offers a more intuitive programming model compared to rake, and has a more full-featured set of CLI options parsing capabilities. Most importantly, while rake tasks are notoriously tricky to unit test and require boilerplate to do so, thor commands can be unit tested like plain ruby methods.

This PR adds a remote.thor helper to tomo (similar to remote.rake) so that developers who are using thor to write CLI commands have easy access to them when writing custom tomo tasks.