enhance popup

It was buggy on my browser
Merge pull request #135 from bitzesty/enhance-popup

enhance popup
show formatted duty expression

and mark it as html safe as it may contain `abbr` tags
[71755478] specs for js on frontend

- use `poltergeist` as capybara driver for `phantomjs`
- specs for tabs JS and popups
- tell `VCR` to ignore *localhost* requests (`poltergeist` uses a random local port to talk to `phantomjs`)
[71755478] set `default_url_options`

so that specs don't complain about this
Merge pull request #134 from bitzesty/71755478-js-specs

[71755478] specs for js on frontend
Merge pull request #136 from bitzesty/measurement-unit-abbreviation

show formatted duty expression