Fixes some missing translations and correct some i18n issues etc. 

A subset of small updates, they are independent from each other and you may cherry-pick those you like.

- [x] Fixes some missing translations and correct some i18n issues.
- [x] Let Travis tests with different rubies.
- [x] Updated README and (c) year. Also add badges for Travis and Code Climate. I find the link to the page about contribution info not being very helpful when someone would like to do a quick patch, so I think this contribution info are more suitable for extensions (I believe it was originally written by @jdutil).
- [x] Use bin instead of script folder for Rails4 (should ofc not be cherry-picked into non-rails4 branches).
- [x] Update dev dependencies + cleanup.