Adds $egChameleonExternalStyleModules / $egChameleonExternalLessVariables

- Enables to register external modules via LocalSettings
- Enables to register external less variables via LocalSettings
- Adds a SetupAfterCacheTest

$GLOBALS[ 'egChameleonExternalLessVariables ] = array( 'key' => 'value' )
$GLOBALS[ 'egChameleonExternalStyleModules' ] = array( module => path )

$GLOBALS[ 'egChameleonExternalStyleModules' ] = array(
 'fixes.less' => __DIR__ . '/skins/chameleon/styles/'
);

Change-Id: I842217aa7a17ad29da15c4b0a0bfd91abd16f484