Implement input type MediaSelector

[alansemenov]

We need a new input type called "mediaSelector". It will be similar to current content selector but will only list content of type media and will have an option to upload new content directly from the input (like image selector).

Requirements:

• Should look and behave like current ContentSelector input type: flat mode by default, icon to switch to tree mode
• Dropdown should only list content of media types (see api.schema.content.ContentTypeName.getMediaTypes()) - this must be filtered on the server
• Should support all of the config options of ContentSelector. allowContentType should be applied to the list of content that is already filtered on the server (if I want to limit the list of media types to only 'audio', for example).
• Should have Upload button to the right of the input field
• Upload dialog should only allow files of media type
• Uploading a new media content should automatically add it to the list of selected options (and to the dropdown, of course)
• The list of selected options should look and behave like it does for ContentSelector