Allow multiple array formats in config in addition to serialize(array())

[SagePtr]

This change allows to use multiple array formats in config file.

Previously, the only one notation was this:
define('OPTION', serialize(array('value1', 'value2', 'value3')));
Now it's allowed to also define array directly (PHP 7.0+):
define('OPTION', ['value1', 'value2', 'value3']);
Or use JSON notation:
define('OPTION', "['value1', 'value2', 'value3']");
Or use comma-separated list:
define('OPTION', 'value1, value2, value3');
Or if array has the only one value, use it directly (if it doesn't contain comma):
define('OPTION', 'value');

Empty string is automatically converted to empty array:
define('OPTION', '');

Serialize(array()) is also allowed and checked first (if string is passed), so backward compatibility with older configs isn't broken.