Update engine and dev dependencies.

So it play nice.
Add missing assets manifest files.
Add config for Travis.
Add license and contributing docs.
Update prawn doc.
Refactor spec support.
Add support for Rubocop and Hound CI.
Major refactor for master branch.

- Move settings to own configuration page.
- Compact pdf templates to single files with readable updated syntax.
- Update all locales to match new structure.
Update readme.
Add locale for :sv
Add locale for :fr
Use correct svg badges.
Correct menu hook for Spree v3.0.0.beta
Controller is not a decorator.
Update admin settings layout for Bootstrap.
Change font_scale option to font_size.

Font scale made no sense for Prawn where fonts not in em but in px. Set
reasonable range from 7px to 14px.
Move print buttons into order tabs.

Filling title space with buttons will break layout quick. Using
Glyphicon ‘save-file’ would look nicer but current Spree version of
Bootstrap do not have that one.
Ensure settings can be set with preferences param.
Higher timeout for Poltergeist to avoid fail rand.
Move slips to bottom in list.