Make Node-Manager Download-Resource Component extensible.

Problem:

• Downloading files to a local machine/node is called "resource-localization".
• There are two components that perform resource-location (PublicLocalizer and ComponetLocalizers)
• Both components utilizes FSDownload.class to perform their downloads.
• We need a custom implementation of FSDownload.

Solution:

• With this change, we make FSDownload.class extensible by wrapping it in a new ResourceDownloader.interface
• We also update the PublicLocalizer and ComponetLocalizers to load ResourceDownloader rather than FSDownload.
• NOTE: We use reflection to load the right implementation during runtime.