fix inconsistent capitalization of sign-up/sign-in links

* merged latest upstream master
* made consistent capitalization of all Sign-Up and Sign-in links
* added links:sign_up: translation placeholders for all languages (need translations)
* added general:or: transations for all languages
* all oauth providers are listed in Home#index 'Contribute' section
* added ApplicationHelper#list_friendly_text method for the previous feature
merge latest upstream master
Merge branch 'sign-up-links' of github.com:bits4commits/bits4commits into bits4commits-sign-up-links

Conflicts:
	config/locales/ru.yml
Merge branch 'bits4commits-sign-up-links'