Customize error message for Ember.Adapter

https://github.com/ebryn/ember-model/issues/118

Added class name to error messages.
Merge pull request #169 from seeweer/issue_118

Customize error message for Ember.Adapter
Added posibility to find record with id 0.

https://github.com/ebryn/ember-model/issues/156

There was a small bug on buildURL method. When id was 0 buildURL skipped creating url with id.
Merge pull request #170 from seeweer/issue_156

Added posibility to find record with id 0.
Refactoring fetch