janus-gateway: new package

[Thomas:
  - Rename patch to the proper naming convention, and add a
    description to it.
  - Add mandatory dependency to OpenSSL.
  - Make the dependency on libwebsock optional.
  - Remove select of host-gengetopt, since this package no longer has
    a menuconfig option.
  - Add missing toolchain option dependencies inherited from selected
    packages.
  - Add proper Config.in help text.
  - Fix the .mk comment header to the proper format.
  - Use the github function and remove the unneeded SITE_METHOD
    variable.
  - Add support for optional Opus and Libogg support.
  - Remove hash file, since the package is fetched from github.]

Signed-off-by: Gregory Dymarek <gregd72002@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>