Small improvements in Config class

• Loading of config files is now done with an absolute path which is quicker in php
• better exception message if config key not found

Index: php/src/common/Config.php
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35c35
< include_once 'config/container.php';
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> include_once realpath(dirname(_FILE_) . "/../../config") . '/container.php';
37c37
< $localConfigPath = realpath(dirname(_FILE_) . "/../../config/local.php");
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> $localConfigPath = realpath(dirname(_FILE_) . "/../../config") . '/local.php';
64c64
< throw new ConfigException("Invalid Config Key");
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> throw new ConfigException("Invalid Config Key " . $key);