fix translations in _social.html.erb

* Should use Spree.t as of ab06b36db2c9f4cf0c46e1905bf4325eec57d52c
* Fixed an incorrect translation key
Remove optimistic lock from inventory units.

Fixes #3238
Fixes #3367
Revert "Remove optimistic lock from inventory units."

This reverts commit 531688404d29f64a81c254262670877e1e9ff3cc.
Fix password fields being visible, test Twitter authentication

Conflicts:
	app/views/spree/shared/_user_form.html.erb
added path_prefix preference

Fixes #93