videoplayback proxy: check if proxy needed for proxying

[unixfox]

For most video sending the data through the same IP address that was used for generation is not needed.

But some do like music videos or else.

In order to avoid consuming some proxy bandwidth, we should internally try if proxy is needed. If that's the case then we can add a parameter like "proxy=X.X.X.X" to the videplaybackurl. If not we don't add such parameter.

Related to #5