Changed elasticsearch AR primary key handling

now supports mapped primary key when _id is part of source with an
alias.
reverted primaryKey of elasticsearch to be array again

meet the AR interface requirements.
improved error reporting
Update yii.php
Italian Translation Typo Fix
Update Language Translation
Fixed italian translation
Updated copyright on title

I assume you’d want this to be updated to 2014.
Edited existing content, sketched out "Creating Your Own Behavior"

Undoubtedly will need to update “Creating Your Own Behavior” to reflect
changes in Yii 2.
Added translations for danish language
Merge pull request #1871 from Theill11/danish-translation

Added translations for danish language
added polish translation
Merge branch 'master' into polish-translation

Conflicts:
	framework/yii/messages/config.php
fix languages list in messages config
Merge pull request #1873 from nineinchnick/polish-translation

Added polish translation
Type fix
Updared extensions guide to include info about PSR-4 autoloading
Merge pull request #1877 from plusodinminus/patch-2

Type fix
Updated extension guide to suggest stricter naming of packages
Made extensions guide more human-friendly and more specific