download interceptor base

[jjustra]

This should be able to intercept browser downloads of files with given extensions, cancel them and make tasks on NAS.
Unfortunately I wasn't able to test this, as I've got following error in last stage of yarn :

error /mnt/sd/usr/src/nas-download-manager/node_modules/deasync: Command failed.
Exit code: 1
Command: node ./build.js
Arguments: 
Directory: /mnt/sd/usr/src/nas-download-manager/node_modules/deasync
Output:
events.js:291
      throw er; // Unhandled 'error' event
      ^

Error: spawn node-gyp ENOENT
    at Process.ChildProcess._handle.onexit (internal/child_process.js:268:19)
    at onErrorNT (internal/child_process.js:470:16)
    at processTicksAndRejections (internal/process/task_queues.js:84:21)
Emitted 'error' event on ChildProcess instance at:
    at Process.ChildProcess._handle.onexit (internal/child_process.js:274:12)
    at onErrorNT (internal/child_process.js:470:16)
    at processTicksAndRejections (internal/process/task_queues.js:84:21) {
  errno: 'ENOENT',
  code: 'ENOENT',
  syscall: 'spawn node-gyp',
  path: 'node-gyp',
  spawnargs: [ 'rebuild' ]
}