Improve handling of plugin filetypes

In IndexController::pluginpublicAction is a list of filetypes.
The basic filetypes are:

'js' => 'text/javascript',
'css' => 'text/css',
'jpg' => 'image/jpeg',
'png' => 'image/png',
'gif' => 'image/gif',

With VisualReview some additionals are added:

'svg' => 'image/svg',
'woff' => 'application/woff',
'woff2' => 'application/woff2',
'ttf' => 'application/ttf',
'eot' => 'application/eot',
'html'=> 'text/html'

Also was added a new plugin functionality

$this->addPublicFileTypes('image/svg');
$this->addPublicFileTypes('application/woff');
$this->addPublicFileTypes('application/woff2');
$this->addPublicFileTypes('application/ttf');
$this->addPublicFileTypes('application/eot');

which is used in VisualReview_Init::init method.

Both ways should be combined, that means in IndexController::pluginpublicAction the additional types should NOT be added anymore.
But they should come from a plugin internal list (either static in abstract_plugin or from plugin manager) since they were added with the addPublicFileTypes calls there anyway.