Sync phpdoc with interface
EZP-20978: validate required properties
EZP-20978: reload given ContentType
EZP-20978: rewrite condition to be more obvious
EZP-20978: remove temp. variable
EZP-20978: extract methods to make main method simpler

Fixed: createContent(): when field langauge is not set by setting struct property directly
EZP-20978: prevent argument mutation
EZP-20978: extract getting default object states into separate method to make main method simpler
EZP-20978: fixed field not being updated not being validated
EZP-20978: fixed translation value on untranslatable field being passed to storage
EZP-20978: refactored a bit for clarity
EZP-20978: removed deprecated tests
EZP-20978: added tests for __construct(), createContent(), updateContent(), improved existing tests
EZP-20978: remove useless assignment, can't be relied upon and is already checked in the service
EZP-20978: fix content fields being inconsistent with field definition constraints
Added inline comment
EZP-20978: fixed for PHP 5.3