add a download guard for browsers

1.automatically scan downloaded files and then upload unrecognized files to cloud analysis

2.show the popularity of the downloaded files

  1. cis already does this
  2. cis had this (threatcast) but was removed in v5. it was said by comodo that it was going to return redesigned but i havent heard about it since.

https://forums.comodo.com/empty-t62482.0.html;msg441215#msg441215