Major refactoring of File source
Major refactoring of File source

 * Add support for File.store
 * Remove nearly useless #initialize
 * #uri returns a useful URI when constructed from an existing file
 * #filename defers to existing metadata before contributing
 * Cleaned up #file

ishwinder/enbake_attach,cch1/attach,ishwinder/enbake_attach,cch1/attach