Looking up stock location by the admin name as well

fixes #5484
Add spec for looking up stock location by admin name.
Remove spec invalidated by https://github.com/spree/spree/commit/a13524a6cfd363c441ff1607a584a3be07e1124f now creating shipments.
Do not allow leading or trailing dot(.) in the first part of email address

Add rspec for email validator

Fixes #5483