Setup rspec-guard

[banukutlu]

I started using this: https://collectiveidea.com/blog/archives/2017/02/09/guard-is-your-friend watched files for changes and runs test automatically.

Originally posted by @cdmo in #69 (comment)

Also integrate guard with our Procfile.dev to run both rspec and niftany.

[cdmo]

thanks for adding this.

[cdmo]

on hold for now, guard-rspec doesn't work with rails 2.5 yet, see guard/guard-rspec#403

[cdmo]

Removing milestone. Just check manually.

[cdmo]

I'm pretty satisfied with our current state of rspec test execution locally.