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
Add Chinese translation

Signed-off-by: qiansen1386 <qiansen1386@gmail.com>
polish the Translation
Continue to polish chinese Translation. Fix all the issue mentioned by @samdark. Removed all comments.

Signed-off-by: qiansen1386 <qiansen1386@gmail.com>
Polish Chinese translation. Symbols

Signed-off-by: qiansen1386 <qiansen1386@gmail.com>
Correction of chinese core message translation.

Signed-off-by: qiansen1386 <qiansen1386@gmail.com>
Update yii.php
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
And a bit more human-friendly extensions doc
Typo in MessageController [skip ci]