Refactor + specs.

Refactor for master branch.

- [x] Move settings to own configuration page + add new preferences.
- [x] Compacted pdf.prawn templates to single files with much more readable syntax (now they are easy to copy for custom slips -before it was just plain confusing).
- [x] Add test environment + specs.
- [x] Update all locales to match new structure (`:de` and `:es` still need work).
- [x] Add `:sv` and `:fr` locales.
- [x] Merged `README_prawn` with `README` and updated documentation.
- [x] Add `LICENCE` file.
- [x] Add Travis and Code Climate.
- [x] Add new style gem version inspired by rails. 
- [x] Bump to 3.0.0.alpha.

Note: need to add more tests, but 0 - 84% coverage I believe is a start.
Known bug is that Settings don't seem to save boolean checkbox values.