Improve default UserValidator behavior[4.0.0 beta 2]

[gabrielalmeida]

Hi, some features not added to #311:

• Reordered validations – since a validateIsUnique or validatePassword message should not be key overwritten by validateAttributes as this last one is probably a less relevant error message
• Now all validations are called even if one of them fails.. So all validation messages are sent at once.
• validateIsUnique method now sends key to attachErrorMsg and also check for errors on each $identity field at once

🍻

[coveralls]

Coverage remained the same when pulling ddb91c4 on gabrielalmeida:huge-update into 07d1bda on Zizaco:huge-update.

[coveralls]

Coverage remained the same when pulling c2ada2b on gabrielalmeida:huge-update into 07d1bda on Zizaco:huge-update.

[coveralls]

Coverage remained the same when pulling c2ada2b on gabrielalmeida:huge-update into 07d1bda on Zizaco:huge-update.

[Zizaco]

@gabrielalmeida Nice contribution! Thanks