Fixed issue where addObserver was getting called w undef prop

Newer Ember versions seem to be bitten by this.
Merge pull request #118 from machty/null-add-observer

Fixed issue where addObserver was getting called w undef prop
Fix Travis
Merge pull request #132 from dockyard/lr-travis

Fix Travis
Mention the convenience property `isInvalid`
Merge pull request #139 from f3ndot/patch-1

Mention the convenience property `isInvalid`
Fix typo for isInvalid
Merge pull request #140 from f3ndot/patch-2

Fix typo for isInvalid
Merge branch 'lr-remote-validator' of github.com:hysios/ember-validations into lr-remote-validator
add uniqueness validator to support i18n